Mesa spent 9 million and got some CRJ200's and misc ground equipment out of the Midway deal. The certificate was returned to the FAA when it went defunct.
Gotta keep it flying to keep the certificate valid. This was why Freedom Airlines had 1 or 2 Beech 1900's on it for a year doing minimal service for Mesa Air Group . . . to keep the certificate active (lord knows Mesa dosen't need 2 certificates to fly 1900's).
Freedom is now being "retooled" to fly ERJ's for MAG as Delta Express . . . it IS ALPA, and ALPA will NEVER, EVER, EVER sign off on any subsidiary of Mesa to fly 737s. Midway is not an option. MAG, in it's current embodiment, will never fly narrow bodies . . . so watch for a new "investment group" to move in that direction (with Mesa owning 49%).
For a list of valid (re: non-defunct) operating certificates:
http://ostpxweb.dot.gov/aviation/certific/certlist.pdf#search='Certificated%20Air%20Carriers'