I’ve never once had DL offer me downgrade compensation for IRROPS (courtesy after the fact yes) but it’s always been the following unless it was explicitly an IDB situation:

a) We can keep you in F / C+ but can’t get you there until tomorrow night

or

b) We can get you there tonight but it’s main cabin only

And unless they offer you specific comp, you are voluntarily accepting the downgrade in option 2 so they owe you nothing (unless EU based flight).

This is hard coded into the app too. If IRROPS happens it’ll show you all of the future flights you can move in your ticketed cabin or tell you that other flights are available but in a different cabin (but without a refund offered)