A FlyerTalk Posting Legend
Join Date: Sep 2009
Location: Minneapolis: DL DM charter 2.3MM
Programs: A3*Gold, SPG Plat, HyattDiamond, MarriottPP, LHW exAccess, ICI, Raffles Amb, NW PE MM, TWA Gold MM
Posts: 100,417
IIRC if you don't arrive late, DOT regulations say that you're not owed any IDB compensation. So the airline could do an IDB and the only "cost" to them would be reporting the IDB and having their statistics look very slightly less good.
OTOH, since in this case there would be a change of carrier from mainline to a regional affiliate, the OP would be entitled to a full refund or rebooking on another carrier/routing that's acceptable to both the airline and the passenger.