Well, I do wish I were going to the next Dead show, even if, without Jerry Garcia, they’re no longer Grateful. 
In addition to Genesis, I can think of another 70s band that didn’t become mega-popular until after their most distinctive band member left, namely (can you guess?) …
… Pink Floyd after Syd Barrett.
It just wouldn’t be The White Stripes without Jack White, but that’s just my opinion 
Man, that’s the second post in two days where I was beaten to the punch while writing. Gotta learn to use preview!
No Michael Stipe; no REM.
No Shirley Manson; no Garbage.
No Anthony Kiedis and no Flea; no Red Hot Chili Peppers.
The Who is still The Who with just Pete Townshend and Roger Daltry–but just barely.
See, but if you added Slash, it would work. But Slash alone couldn’t do it either. Tis a complicated world.
Gargoyle, please correct me if I am wrong, but you ARE saying here that Sabbath and AC/DC are STILL good, even without their original frontmen, right? This is what I took it to mean but there does seem to be some confusion on that point. My take on AC/DC is that Malcolm and Angus are the indispensible ones.
And I think Pearl Jam would not be the same without either Eddie or Mike McCready.
Some more:
No Rivers Cuomo; no Weezer.
No Bono and no The Edge; no U2.
No Mick Fleetwood; no Fleetwood Mac (obviously).
Speaking of which…
How about Fleetwood Mac after the successive loss of two frontmen: Peter Green and Bob Welch?
rockle I second your vote for Pearl Jam. Eddie Vedder can’t be replaced. Nice to see someone else who gives McCready the credit he deserves.
I’ll add it’s not Tool without Maynard. Too haunting and unique of a voice to replace. But they wouldn’t be the same either without Danny Carey on drums. Much too talented and original to replace with any old drummer.
I second that. Steve Harris IS the backbone of Maiden.
Not a bad bass player either. 
Nice to see some postings about Martin Barre - guitarist of Jethro Tull. Yes, he may not be the flashiest guitarist but his solos are well-thought-out (as opposed to someone else just playing speed for speed’s sake).
Think about that guitar solo in “Aqualung” - one of the best constructed rock and roll solos in R&R history IMHO.
(“It’s reuired reading at the Academy” as they say in Star Trek LOL)
I would say that Gossard is Pearl Jam. Also, A Perfect Circle is basicly Tool with different players, so you are pretty much right there. Maynard is the draw.
Fleetwood Mac w/o Christine McVie doesn’t work for me.
Electric Light Orchestra w/o Jeff Lynne? Nope! So screw you, Bev Bevan.
The Beatles wouldn’t work without all four members.
No Lindsay Buckingham=No Fleetwood Mac. For me anyway
I agree that No Jeff Lynne=No ELO.
what he said
There is no Pearl Jam without Eddie Vedder.
I gotta agree with Dark Canuck on Tool.
Additionally, it wouldn’t be Nine Inch Nails without Trent Reznor. (duh, as he does almost all of the studio work himself and hires bandmates when he tours).
I’d say Porcupine Tree is Steven Wilson.
I’m gonna go out on a limb here and say no Metallica without Cliff Burton. And Justice For All was a decent enough album, but it was just the first step down a slippery slope to the utter cheeseball hell in which they now dwell. They suck.
But I do have to disagree with people who say that Roger Waters sucks. Come on, guys. You might miss Syd Barrett, and you may not personally like Waters, but he’s a gifted lyricist, probably one of the best in rock, ever. I think that the post-Barrett Pink Floyd with Waters is easily one of the greatest rock bands of all time. JMO, YMMV, I guess, somehow…
No.
A-friggin’-men. Ray Manzarek needs to stop leeching off a guy who’s been dead for 31+ years now. Great keyboard player, to be sure, but based on his legacy of using Jim for his own personal aggrandizement, I think he needs to go away.