Chip,
My understanding was that US itself wanted to get out of the turboprop business, meaning mainline, Allegheny, Piedmont and PSA would no longer fly turboprops. I've been somewhat assuming at least one affiliate carrier would remain to serve some of the smaller cities where RJs simply don't make sense or can't be handled (due to runway lengths, etc.). Also, no turboprop flying would mean many of the smaller cities US mentions in its PIT impact study would lose service no matter whether the hub stays or not. For example, I seriously doubt Altoona or Latrobe really can support RJs. Also, many of the MCI turboprop cities also come to mind.
The way I see things unfolding going forward is U will consist of mainline, PSA and MDA, with Allegheny and Piedmont ultimately merged into PSA in some fashion. Then, Air Midwest, in light of its ownership by Mesa, will remain as the turboprop carrier to serve the smaller markets where RJs are not necessary. Colgan might remain as well -- many of their routes I wouldn't classify as "RJ routes".