In other words, anything could have happened to it. It could be part of the Federation, but then again, maybe not. If it still exists in its current form, I wonder if there is "Federation space" on all sides of it now, or if it's in an area that's kind of left alone in the 24th century... Even at only 100 light-years away, the vastness of interstellar space may mean that it's relatively left alone.
It's estimated that there are roughly 15,000 stars
within 100 light-years. We now consider it likely that most stars have planetary systems. If Earth and the Federation had enough ships to visit an average of one new star system per week, it would take nearly 300 years just to visit them all even once. Exploring them all in-depth would take a lot longer.
So yes, it's quite likely that even in the 24th century, a lot of "nearby" space is still relatively unexplored or at least not routinely visited. And with 15,000 star systems, there's certainly room for a number of independent states to exist as enclaves within nominal Federation territory.
As I've said before, since space is mostly empty, it doesn't really make sense to think of an interstellar power's territory as a solid volume. More realistically, it would be the space immediately surrounding its member systems plus the regularly travelled/patrolled space lanes connecting them, more a tree or lattice structure than anything else. So different powers' territories could easily interpenetrate without really intersecting. Space is certainly roomy enough for it.