"Space is big. You just won't believe how vastly, hugely, mind- bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space."
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.