Regardless whether it's Monahan, Drouin or another short-term 3C who is signed, Dvorak going in a package for a better center makes sense.
If there's a team willing to take Dvorak's contract without retention this summer, the Habs should seriously consider pulling the trigger if the return is decent enough when compared with Dvorak's optimal worth at TDL 2025. Being an asset in a Dubois deal or fetching at least 2nd round pick on his own, for instance.
If Dvorak's traded, I wouldn't exclude signing Monahan on a bonus-structured contract; amongst the UFAs the Habs can plausibly sign this summer, he remains one of the best mentor available for a young core.
This being said, whereas there's no real urgency to trade Dvorak (unless his upcoming no-trade-list is a considered a serious issue), I think it would be very opportune to get rid of redundent wingers - Hoffman and Armia - ASAP to make room on the NHL roster for young wingers to start integrating the core next year.