Many times Star Trek has taken us to the future only to reset the status quo at the end of the story arc. Tapestry (but in reverse?), that time Voyager crashed in the ice, and all that.
How likely is it that Discovery went to a mutable future, just one of many, especially with the Temporal Cold War, Carl, Q, Trelane, Janeway, the HMS Bounty, and any number of other temporally active agents out there in time? How locked in is the 32nd Century?
It’s just a future, and can be changed. I’m not aware of any objective in-universe measure of what is and isn’t the prime timeline, it’s really just what the writers choose to depict as such, which events are altered by time travelers and which ones stand. Since we’ve seen a full two seasons in this version of the 32nd century, it’s more likely that future shows will try to keep consistent with it, but it’s also possible they’ll be “retconned” into an “alternate reality”.