I think we are all speculating at this point but merger between the three is unlikely. Morelikely scenario would be Compass merges with either Mesaba or Comair and then sold off. DAL would raise cash and have the rest to whipsaw against. Merging Mesaba with Comair is unlikely because both has too many senior pilots who would object to the merger whereas merging Compass with Comair or Mesaba would be relatively easy.
Last I heard there are 35 to 37 more 76 seat RJs for bidding in the DAL system. DAL has B777 on order and NWA has B787 on order.
Early buyout for senior Mesaba pilots makes sense for the management as Mesaba has many senior pilots who has at least 20 years in with Mesaba and getting close to age 60 or over.