In general, sitcom characters tend to end up staying largely the same or they get more successful and accomplished as the show runs. Are there examples of shows that do the opposite and have a main sitcom character deteriorate in economic well being as the show progresses?
Shows in which the main character is rich for the first 10 minutes of the pilot and then suddenly become poor don’t count.
That doesn’t sound very conducive to comedy, does it?
Not really the same, but Edmund the Black Adder, [del]heir presumptive[/del] second in line to the English throne becomes Lord Blackadder a favourite of the English monarch, then a servant to the prince regent of the UK, before being a captain in the British army.
Seinfeld - the main characters all ended up on prison.
Doesn’t Reg Perrin end up giving up everything again at or near the end of his series?
In Lucky Louie, the family was already poor, but towards the end Louie quit his job. In the following episode, IIRC, his wife (a nurse, the chief breadwinner) left him, so Louie was pretty much fucked.
To being King Edmund III and eventually ruler of the known universe. So no. 
IIRC, Sam originally owned the bar on Cheers, and after several seasons sold it, and promptly blew through all the money – and eventually came back to ask for a job pouring drinks and supervising the servers like before, only as a hired hand.
So they could do the will-they-or-won’t-they stuff again – but without just doing a flat retread of Diane’s storyline, because now he was an employee pursuing his boss; and she was pursuing her boss, who seemed to genuinely enjoy having Sam around. So it opened up storytelling possibilities, after they’d spent years on yep, he owns a bar.
(Granted, that maybe doesn’t technically count for this thread since IIRC he got the bar back years later – but I figure it answers your question; if you eventually need some new ideas for the main character in a sitcom, it seems you can put him in a better financial situation or a worse one as you prefer.)
The economic situation of the Bluths on Arrested Development got worse and worse as time went on, although they all tried to keep living as if they were still rich.
The Pruitts of Southampton had that as the basic premise, and things didn’t get any better over the short run of the series.
Earl had several reversals of fortune on My Name Is Earl, first winning the lottery, then spending all his money and ending up in prison for a while.
On It’s Always Sunny in Philadelphia, siblings Dee and Dennis Reynolds came from a richer background, but for various reasons don’t have as much money anymore. They weren’t shown as rich at the beginning of the show, but they seemed more comfortably middle class, but seem more working class now. Their father Frank does still have money because of his business dealings but basically chooses to live in squalor.
Lucky Louie is a great example and I wish it got more than one season so we could see how far into squalor Louis CK was willing to take it.
I don’t think any of the castaways on Gilligan’s Island improved their lot during the regular run of the show. The Skipper (boatless) and Ginger (several years out of the public eye) would have certainly been worse off at the end.
I know that there were people trying to claim the Howell’s fortune during the run of the show. Did any of those succeed?
The Professor would have fallen behind in all the fields he was an expert in. Would have quite a chore re-establishing his career afterwards.
Mary Ann would be about the same.
Gilligan, OTOH, might be able to make a killing after rescuing selling all those indestructible hats and shirts he seems to have invented.
The Professor will be just fine. Is cancer a hole in the side of a boat? No, it’s not. Therefore, the Professor can cure cancer with coconuts.
The current sitcom Schitt’s Creek has this plot. A megarich family (Eugene Levy, Catherine O’Hara, Dan Levy [Levy’s real life lookalike son], Annie Murphy) whose fortune came from video stores loses everything due to the collapse of the video market, an embezzling business manager, and an IRS debt and ends up living in a fleabag motel in a tiny town he once bought as a joke.
Ellen- the Ellen Degeneres sitcom in which she made history by coming out- began with her owning a successful bookstore which at some point she lost and started working temp jobs.
Both Roseanne and All in the Family (the two best blue collar sitcoms ever imo) had roller coaster financial arcs, with the family sometimes doing okay, sometimes slightly better, and sometimes flat broke.
Schitt’s Creek appears to fall under the “only rich for 10 minutes in the pilot” trope which is different.
Yep. This was addressed in *Rescue from Gilligan’s Island *; he kept trying to invent things only to discover that someone beat him to them.
Bad show with great theme song.