From what I have heard:

There would be a 10% reduction in the amount of flying being done by Delta, as the route structure does have some overlap.
Skywest from what I understand would be ok as their contract has already been signed during the bankruptcy the other regionals are kinda up in the air.
There might be a reduction in 50 seat flying with an increase in 70-90 seat flying...again all rumors I have heard.

My own thoughts...US Airways doesnt even want Delta, they are trying to get United in a bidding war with them so US Airways can then turn around and try and buy Northwest.