I can't see him just prematurely ending the game. He's never shown signs of slowing down, he only generates more and more content each release.
And while some people aren't loving the logistics behind some of the plot points (can't please everyone), I think his characters and pacing have been pretty consistent, and nothing feels rushed or significantly out of place.
He's stated more than once that he's already planned out his overall story, and I think we've all worked out he puts some plot points in motion well before they become fully apparent. So he must have a decent method of tracking his characters and story; he's not just winging off the top of his head.
He's said from the beginning that he has a very specific plan for the game, and while he often gets carried away and adds more detail than he initially intended, I don't see why you would get the impression that he can't keep this up (the fact that he gets carried away and produces more than he intended only shows his enthusiasm is genuine, if he starts half-assing it, then I'd accept we were nearing the end).
I wouldn't hold him to the standards of a typical developer, he's very unique in that his drive hasn't wavered one bit. The guy even got COVID and hardly skipped a beat.
After episode 8 was released (late last year), he explicitly stated,
"Right now, we have reached an approximate midpoint of the main story." I can't see why he'd just outright lie about that; patron's are gonna keep paying right up until the end.
And only a few months ago, when questioned about "burn out", he answered it pretty definitively: He still loves making this game.
To Quote him (from the last Q&A - Feb this year):
"The motivation is always there since I love creating the game. I was prepared beforehand that the development would be this long, which also helps. Also, looking forward to episodes that I know are coming soon keeps me going. There are many scenes I can't wait to write, and when the time comes to write them, it's like a big payout."
He has consistently had this attitude towards his work, so I'm really quite convinced he will follow through with his plan, and all evidence so far points to the game being longer, not shorter, than originally intended.