I personally think that you will see the 50 seaters flying for a lot longer than most people speculate.

You can pick up a CRJ-200 airframe without engines for less than $100K these days. You can probably get some mid-time CF-34's for less than $600K a pop.

That makes for a very cheap platform. I don't even think that increasing oil prices will put a dent into it any time soon.

You will see those flying as long as airlines can staff the equipment and there are no gate space limitations in the hub airports...