They still have space to sign him to a contract. I don't think its a given that the Pistons would match, since they have Josh Smith (who's naturally a 4) who is hard to trade. Monroe is very underrated. He'd have to improve on his mid range game, but that's doable.
Would rather have smith honestly. Easier to acquire and better defender at the PF spot. Would just need to make him the 4th offensive option.
Why do you think the Pistons haven't given him an extension? Because they know he doesn't fit with Drummond.