The problem I have with planing 'endings' is that real stories never 'end'. A parent's story doesn't end when they have children, it just becomes a different kind of story, and the same goes for a child's story when they grow up, or they get married, or have kids, or their parents die. Normal stories only 'end' because of formatting constraints and audience limitations: no one will watch an 8 hour movie, and precious few will sit through a three or four hour one. Therefore, the story must 'end': but with our format, this is not the case. Consider the Diskworld series. Yes, it 'ended': because the author, (Sir Terry Pratchet*,) DIED! Each book in it had a specific arc, but most of the characters reappeared in a half dozen books at least, many more-or-less picking up about where the last one left off.
*(God Rest His Soul.)
Now consider a fictional book series, "The Tales Of Genma's Daughters*". This series from the EXALTED universe was written by a woman and spanned 10 Sylmarilion length volumes, then she died. However, in EXALTED, death does not always mean the end for a person's story: the writer became a ghost, and continued writing the story for over 300 years! It now spans 270 Sylmarilion length volumes, and is generally only read by the Exalted or other ghosts, who have a lifespan and resources such that they can buy a complete collection and devote four hours a day to reading it for a decade in order to catch up from the beginning, or who've been following the story for decades already...
*(Which by the "current date" of EXALTED is actually about the titular characters Great-Great-Grandchildren...)
This is where I see some of these CHYOA stories ending up: thousands of chapters deep and involving the grandchildren of the original main characters...
As for not branching, I find that doing so weakens my ability to update consistently: the more I branch a story the harder it is to keep the chapters coming. Like most authors, I'm all about the narrative, the more the story branches, the less I can get done. Maybe when it reaches an 'end' I'll go back and start a new thread from an earlier point, but until then, I write linear.
(Also, remember, depth is displayed on the front page: breadth, isn't...)