You're right. He fixed the leak. Worf "made things the way they were SUPPOSED to be". He blatantly understood, in a dumbed down way, what Guinan understood in "Yesterday's Enterprise", that there is a certain way that this certain timeline is supposed to be, and it needed to be repaired to, in his case, stop him from shifting between all of them, or in Guinan's case, prevent a reality where the Federation and Klingons were in a continual war. I present to you a reality where the Federation is dead. What would you do?
You're working under some wrong assumptions regarding how the Prime timeline and the Abramsverse relate to one another.
When Nero arrived in 2233, it created a new timeline that runs in parallel to the Prime timeline. It created a branching point or a fork in the road. To the right the Prime timeline goes on as if nothing happened, to the left the Abrams timeline was created and Nero wreaks havoc.
The writing team used the concept from Parallels
to keep both the Prime timeline intact and create a new one. They essentially used the concept to create a soft-reboot of the franchise.
If they destroy Nero before he ever creates the new timeline, they destroy the new timeline but it has no bearing on the Prime timeline in any way. It is still chugging along in two different forms in the novels from Pocket Books and the game Star Trek Online
, which both also have had to branch off at some point because they are incompatible with each other from a story and continuity standpoint.