I think people get unrealistic expectations of long series that don't have breaking points, as opposed to when an author spews out a book or trilogy, wraps most things up then starts over.

Anyway there aren't really that many series that suffered "Author Existence Failure" quite this way. Most wrapped the series up and had been pondering some extensions - like Douglas Adams Hitchiker's Guide, Roger Zelazny's Amber, Herbert's Dune, or Asimov's Foundation - rather than really having a series left undone, a few loose threads and teasers not really counting.

Personally I'd say it works better when the author built a big multi-character and flushed out world, because then follow up authors can simply pick a fairly secondary or new character and have original main characters show up for cameo's or mentions. Harder to do with more character driven books, especially when they center mostly on one or a small handful of main characters. I don't think anyone would have much problems writing in Niven's Known Space series for instance or McCaffrey's Pern, and there are tons of settings like Star Trek, Star Wars, Star Gate, Warhammer 40k or Doctor Who where the original author/creator isn't even universally agreed to be the 'best one', albeit none of those are famous for their quality.

So I'd say the answer is a 'kinda sort yes'