Many people expect Nistelrooy to stay at Man United and become Amorim's assistant because Nistelrooy showed good performance when replacing Ten Hag. It should indeed be beneficial to both parties, as Nistelrooy can continue his genuine role and it will be easier for Amorim to approach Man United players with the help from Nistelrooy.
But still, it can't be forced, especially if both of them do not share the same vision, so it would not be surprising if instead of getting good results, Man United could end up slumping again.
By the way, Roma is again left without a coach, for the second time since the beginning of the season, too frequent changes also have a bad effect on the team, but it is time to end these experiments with coaches and choose someone from whom they can really expect great results.