DL has already "left" most of DFW...it has dropped DFW as a hub but will not abandon DFW-will still have flights to cities like SLC, CVG, and ATL.
Anyway, even more interesting than Simplifare response will be AA's response if FL (most likely) or B6, F9, NK, HP, or even WN take up some of DL's vacated gates at DFW.