I was thinking of John M. Ford, too, but, come to think of it, he only did a couple of TOS books. Ditto for Janet Kagan. And, on the editorial front, you have David Hartwell, who launched the whole Pocket Books STAR TREK line back in the eighties, but he had moved on from Pocket Books by the time TNG came along.
Nobody has ever said anything about there being any kind of a predetermined end point for the books, and since they don't really have any kind of main arc that they are following I don't see why they would need one. The arcs that the books do usually just lead to new arcs once they are done, so I don't see any reason to think they can't just keep going on indefinitely. As long as we continue to get books as good as they have been lately I wouldn't want them to end, and as unless the sales suddenly drop off drastically I don't see any reason to expect them to. Even if the sales did drop, I have a feeling we would just see the books revamp a bit, rather than just end outright.
I know I've asked this before but how far chronologically will they get if they continue indefinitely?
How long is a piece of string, both @Greg Cox and @JD have answered that answered pretty well. There is no end date as yet.
I think it's literally impossible to answer that. Like I don't even know how you'd answer that conceptually.
It's theoretically possible for something to be indefinite but finite, like the limit of an asymptotic curve as X goes to infinity. E.g. if you accelerate indefinitely, in theory you can keep getting incrementally closer to the speed of light but never reach it. In the case of Trek Lit, though, it would have to be something like, say, how 5-year-mission novels can't go past 2270, or TOS novels featuring Kirk can't go past 2293 (discounting the TNG-era Shatnerverse), or something like that. But that only really works for series that don't have a continuous serial narrative.
We'll continue to tell adventures that unfold over the course of a three-week period in early 2387, for the next twenty-seven years. But it'll be the same eight stories, repeated over and over, with each iteration bringing subtle modifications to the plots until they all begin to form a single, coherent arc with the books published around 2043, that eventually wraps up with Q and Picard sitting on a beach, drinking rum and watching a sunset before Picard heads off to join Tasha Yar and the Enterprise-D at McKinley Station. Welcome to Star Trek: Revenge of the Typhon Expanse. It's about Time. Really.
Haha, yeah, fair. Supremum's the word you're thinking of for that, by the way. Or infimum for a limit you're approaching from above but never reaching.
I don't mean to be rude, but why is this such a big deal for you? Can't you just enjoy the stories we're getting now, without getting all worked about if or when they'll end?
It's probably fair to say that they won't go past the heat death of the universe. What's that? Alternate universes??
In Dr Who, the heat death of the universe occurred in 1981 (Earth time), when the Fourth Doctor was falling off radio telescopes...
Bottom line: they'll keep going for as long as they sell, or for as long as the publisher has the license, whichever comes first. This isn't THE LORD OF THE RINGS or THE WHEEL OF TIME; we're not writing toward some predetermined ending. It's an ongoing, open-ended franchise, like Nancy Drew or the Hardy Boys, which will keep on going for as long as there are readers who want new STAR TREK adventures . . . Pretty sure that, when Roddenberry first launched STAR TREK back in 1966, he wasn't already thinking about the series finale.
He wasn't paying much thought to the TOS series finale when he was writing "Turnabout Intruder," either...!
This isn't really a 'frustration' but more of a wish. I just finished The Face of the Unknown and enjoyed the focus given to the 'junior' officer and it made me think of the good old 'numbered' series days when we would get the occasional book centered around the adventures of Sulu, Chekov, and Uhuru. Death Count was a ridiculous book but I count it as a guilty pleasure. Traitor Winds and Rough Trails were two others that I enjoyed. There were more but I can't think of the titles right now. Ice Trap maybe? Firestorm? Anyway, I liked taking a break from the big three from time to time and seeing the focus shifted. They were similar to 'lower decks' type of stories. It didn't happen a lot but when it did, I enjoyed it and wouldn't mind if we saw more of that in the future.
Gold Key did it 40 years ago. Of course, it ended in a fencing match between Kirk and his doppelganger from a previous incarnation of the universe where the Starfleet uniform was blue pants.