Cavani is definitely a class. certainly, he and Ronaldo are a separate story for themselves. but unfortunately, both are too old, especially for play in the Premier League, where a high level of physical fitness is required. Plus Cavani is very prone to injuries this season (I think he got hurt again, but playing for the national team). all minutes he missed were either because of injuries or a lack of strength to keep up.
If Man United wants to move forward, they have to give up players who have a maximum of one more good season.
Maguire, as it is, has to play next 10 years. even if he doesn't manage to improve his form or whatever is wrong with him, it will always be able to be a reserve option in "easy matches" when important players need to rest.