How big is the estate? When was the house built? And, most importantly, WHERE in the country is it? Heck, is it even anywhere in the US?
If it is somewhere inhospitable (defined by me as “anywhere it snows”) or if the house is too new (“built after the Great Depression”), it gets sold, and I use the money to buy a Greene & Greene bungalow in Pasadena. Ideally, this one.
Oh, and yeah, keep the staff, or hire new ones at the new location, if necessary.
What I hate more than McMansions built on a small or average sized lot is McMansions built on a largish-medium lot – totally devoid of trees. I’d frankly rather live a little closer to my neighbors, as a lot that big isn’t useful for anything except ostentatious ugliness. You can’t even play lawn games on it because the driveway cuts right through it. Do people actually want these, or is it some sort of regulation that makes them clear cut, or perhaps they can tweak a few thousand out of the sale of the timber from a couple acres?
But an estate big enough to have its own arboretum, vegetable garden, garden, AND an outdoor rec area, that’s ok in my book. Except for the fact that it’s not very walkable even if it were close to a downtown. Maybe if I had one of those, I’d invest in a bicycle or three – much more convenient than a car.
I’d sell the place and buy an awesome condo or townhouse in DC. In a heartbeat.
(Any money left over after the sale/purchase would be used to pay for a parking spot near home. ;))
Fairfax? Fairfax?? 
If I had money and had to get a place around here, I’d pick McLean or Great Falls.
If you live on an estate, then you can “Release the hounds”.
Which, would be cool.
I’d try the life for a while. Who knows, I might like it!
I would, however, want the estate to pay its own way. After all, we’re talking staff costs alone in the million dollar range. I could quite see myself becoming the gentleman farmer.
OTOH managing such a large fortune is going to be a lot of work. It’s likely to be in the form of businesses rather than kilos of gold. So I could use the house for business meetings and the like and my personal life will likely be very busy. So having people to take care of the little things could be very useful.
I would sell the mansion, fire the servants (with a year’s salary) except that I would keep the services of the cook, a cleaning person, and a gardener/groundskeeper (the latter two part time, the first full time). I would buy or build a house on a large tract of forested land with a creek, right around the area I live now (maybe in Los Gatos). The house would be around 5,000-6,000 square feet, custom designed, and would contain a finished attic, a finished basement, at least two stories, and at least one secret room/wing. It would have a kick-ass game room, media room, library, and dedicated area for the cats. This would make me very happy. 
I’m not sure. I definitely wouldn’t want to live in the mansion- I doubt I’d be comfortable with someone going through my knicker drawer, or cleaning up after me. Neither do I want a massive house to live in.
I might, however, keep the place and convert it to some more interesting purpose, while I moved out and got my own little place built to my own specs. Probably some shamefully hippy thing made out of straw bales or something, somewhere in the woods, with two spare bedrooms, a craft room, a kiln, an orchard and space for a few cows and chooks. I’d probably travel a lot as well, and get some hippy friend to live in and look after the critters while I was away, though I could see if any of the mansion staff would want to do something like that for a while if I couldn’t find a reliable enough hippy.
As to what interesting purpose I would put the mansion to- I’m not sure. Possibly make it available for short term rent at a laughably low rate to art and circus groups, and, if it’s a proper fun old mansion, roleplay and medieval recreation groups. Basically, anything I think is kinda fun, and would benefit from lots of cheap space, that I could come and join in at when I felt like it.
Unfortunately for the staff, this would probably mean a lot of them (chauffeur, butlers etc) would be out of a job, though I would be pretty damn generous with severance pay, and any who could be kept on would be if they were happy to work in such a random environment.
I’ll keep the mansion and staff. One of the rooms will be turned into the Mother of All Man Caves. Full size pool table, several pinball machines, TV screens the size of movie screens, awesome sound, wet bar/kitchenette, hot tub, big-ass man chairs, bowling alley, possibly a self-contained and sound-proofed pistol range, gaming consoles, computer space, etc.
The Druidess can do what she will with the rest of the mansion. She’s got good taste and better sense. I suspect she’ll want a Girl Cave with her own toys, will likely set aside part of the grounds for a stable/mini-zoo. The Druidess digs critters even more than Ellie May Clampett did, and with ridiculous amounts of money to indulge herself, I suspect there will not be a homeless or hungry animal in a multi-county area surrounding The Grove*.
And staff is important. I like to be pampered. I might have to fire the current chef, if he or she only cooks that pansy ass Gordon Ramsey crap. Men shouldn’t have to eat like that. And whoever we hire needs to know how to make grits and sweet tea, along with a full menu of manly delights. OK, The Druidess likes some of that fancy crap, so I may keep the chef and hire myself a regular cook to serve the Man Cave.
*Of course my estate will be called The Grove. My namesake is a raiding druid, and my wife is The Druidess. What else would we call it?
Don’t forget to hire a series of accountants to audit the books regularly. With that kind of money comes greed and suddenly your “fortune” has disappeared.
Mansion with library.
And Harem.
I would keep the estate and hold a Hide & Seek tournament every year. Heck, twice a year. With themes. First up, dress as your favourite Tolkien character. Next up, favourite historical figure from the 18th century.
The servants don’t bother me. They are professional servants, I would probably never even see them except for the butler. Isn’t part of his job managing the others so that I don’t have to?
Yes, I’d keep the estate and think I’d died and gone to heaven.
NM
Sell the mansion to a romney, buy a gigantic piece of land on a river in the north woods, build a 1500 sf house and 20,000 sf barn/workshop directly in the center of it and put up some fences. No maid or live-in servants, just somebody to take care of the snow removal, mow back the brush once in a while, and deliver groceries. I wouldn’t want any maids or other domestic staff messing around with my stuff.
Speaking of horse…
The father of a girl my daughter used to ride with was one of the founders of a Silicon Valley company, and made a large fortune at the IPO. he bought a big place just down from the barn, with a helipad so he could helicopter to work, a stable, and lots of space. He bought a houseboat just for the berthing rights. He was having a great time.
His wife, however, hated it. She was stuck dealing with the workers who came in to do the latest renovation, and dealing with people who had to be called to fix any of his toys when they broke. They are both pretty down to earth. He told her to get an assistant, but she didn’t want one. She told my wife “One more damn toy and I’m leaving!” No servants or cooks that I know of, though they could have afforded them.
As for me, I might get a slightly bigger house to have wall space for my books, but I already have rooms we hardly ever go into. I don’t think we could stand cooks or servants. And I definitely don’t want to move - one of the best things about where we live now is that it is really close to everything we need - walking distance in a pinch. 4 groceries, a hospital, a mall and 2 smaller shopping centers, my dentist, my doctor (a bit far, but doable) and more restaurants than we can count. The last thing I want is a place outstanding in its field where you have to drive anywhere. And we have pretty much perfect weather already.
For some reason, a huge mansion has never been my thing. Maybe growing up in the city, I dunno, huge expanses of land don’t appeal to me. I’d prefer sweet ass high-rises on each coast. No butler necessary, but I’d bring someone in every other week to clean up the place, and a chauffeur would be the best thing ever. The amount of money I spend on cab fare is just shameful.
So I’d probably sell the mansion, buy some place I’d rather live in, keep the chauffeur, and reduce the maids’ hours. Hmm, maybe I’d hang on to the chef too.
I’d hire more staff. I’d need a game-keeper, a few ghillies, a falconer or two, assorted grounds-keepers, someone to grind pepper on my eggs in the morning, Ilsa the She-Wolf to flog the pepper-boy when he puts too much on my eggs, a large Swedish and small Japanese masseuse, etc.
Hey, it’s my responsibility as a “jobs-creator” now, right?
I’m with StG… as long as there is a stable, pastures and an indoor arena, I’m good. If not, and there isn’t enough land, I’m selling the sucker and buying a place where I can have horsies.
As for staff, I would have a housekeeper come in a couple times a week, a groundskeeper and stable help.
I wouldn’t want a mansion nor need all the staff. I’d feel bad about firing the staff so would make sure they received better then reasonable severance packages or maybe see if I can arrange for them to stay on with whoever buys the mansion.
I think I’d buy a small New England farm and have a few full time people to run and maintain it. A housekeeper coming through once or twice a week and an on call secretary to handle expenses, appointments, travel plans.
5 bedrooms on a decent sized property. Several of those in various locations. Not a full time staff but a cook would be nice. I don’t need much.