If you look at the comics in the newspaper, you'll find that many of them are strips that have been around for ages. Long-running strips are LOOOOOONG-running strips, often out-living their original creators. The Katzenjammer Kids, Blondie, The Phantom... I think one of the reasons syndicated comic strips were viewed as the end goal for cartoonists for so long was because it was almost a guarantee of a life-long career.
Of course, not every strip continues indefinitely. Gary Larson and Bill Watterson are probably the most famous semi-recent examples of cartoonists who deliberately discontinued their strips at the height of their popularity. And, even more recently, we've seen the official discontinuation of Little Orphan Annie and Brenda Starr.
But there MUST have been any number of comics that also disappeared from a local paper because the syndicate itself no longer distributed it, despite the original creator still working on it. The only instance I can think of where this happened was with Nate Creekmore's Maintaining, which started in 2007 and ended in 2009 when "Universal Press Syndicate has chosen to opt out of its contract" with Creekmore. Though he enjoyed working on the strip, Creekmore stated at the time that it wasn't financially feasible for him to even look for another syndicate. At least relative to other work he was doing. So the strip was discontinued.
I'm aware of that one instance because I was a fan of Maintaining during its short run. I check back on Creekmore's site periodically to see if there's ever any news about A) what he's been doing since then, and B) whether he decides to ever start the strip up again in some other venue. He continues posting scans of pieces he's working on, so it appears he's getting some commission work, which is great. But of course, I'm always disappointed to see reminders on his site about the comic that he isn't working on any longer.
Surely, though, Creekmore isn't the only person in that situation. A formerly syndicated cartoonist who managed to "break in" only to have the rug pulled out soon afterwards. I'm curious how often that happens. I suspect it's more frequent now than it was, say, fifty years ago as there's a seeming need for more immediate results (i.e. lots of papers picking the strips up). But does anyone keep track of how often comic syndicates de-syndicate a strip?