First of all Maguire is a horrible player and should not be played, there isn't a situation where he is the best defender they have, he could be removed and they would have a great team, Varane and that other defender I forgot his name the short one, those two would be good enough, if you put them and then Ronaldo it should work. They have casemiro to play at midfield as well, so that team should be fine enough.
Thankfully Erik ten Hag doesn't prefer Maguire in the starting eleven of important games anymore. He started to choose him in only Europa League games lately. He isn't a reliable defender for any big team at the moment. I think that he might be sold after the end of the season also if they find a better replacement for him. He shouldn't be even the last resort for Manchester United I mean.
If Ronaldo also leaves the team at the end of the season then Manchester United should go for a good striker transfer. They can't continue with only Rashford. Antony has been brought here but he isn't a striker. Some people think that he is here to replace Ronaldo so that's why I wanted to say that. However Ronaldo might decide to stay if Manchester United make it to the Champions League this time.