No, they aren't leaving. United did say that they wanted to shrink 50 seat fleet in half, but then they hired this guy from AA named Kirby who likes regionals and i haven't heard much more about 50 seat planes going away. 50 seat fleet is getting shifted around. Air Wisconsin (who has 65 CRJ200s all in AA colors) just signed a contract with United for 50 planes plus 15 options (so basically they will repaint those planes into UA colors). Eventually, one day, all the E145s and CRJ200s will be too old to keep flying, and they won't be built anymore so who knows what the regional landscape will look like when those planes start getting mothballed.

Now step away from the keyboard and focus on flying. In two years, start looking at this section of the forum again and you'll see that nothing looks the same.