The bottom line is small RJs are going away in massive numbers.
Schedules are being adjusted to fit smaller mainline aircraft into those cities and reduce the number of flights but maintain capacity (most cities). Look at vps, fay, cae, and even AGS. Flying an airbus, 717 or md80 and cut 2-3 50 seaters. Its been happening and it will continue to happen. Delta still has another 30+ 717s to take delivery of from southwest.

United is a few years behind delta so expect to see the same thing. American is jumping on the bandwagon as well.

There will always be a spot for smaller jets, it just won't be the major part of domestic flying any more.