Before starting work on Manchester United. Nistelrooy was working for PSV and maybe this means Nistelrooy is experienced enough to help Manchester United where he played therefor years. Even he had a good performance as the coach of Macnshter United when they were playing against Newcastle United and maybe that's a good sign to say Nistelrooy could help this team even more than Ten Hag
I think since Nistelrooy is familiar with the team the best they can do is to keep Nistelrooy for a longer time to help Amorim if Amorim agrees. Because Amorim is not familiar with the Premier League at all.
I think Van Nistelrooy has left the team. I am sure Ruben Amorim has his own team. He will want to work with his own team and I understand that because he really did a great job with his team at Sporting Lisbon. He will probably bring some important players from Lisbon to Manchester. I believe the Portuguese manager will bring a new breath to Manchester. He has made a good start to his career. I hope he can show us a Manchester United that can play at the top of the Premier League.
Amorim would have wanted Ruud to stay for a while though, like for example to get a report on who looks like how. Remember, this isn't a fifa or football manager game, players do not have ratings written on top of them, nothing is for certain and if nobody tells you anything, all you can base your assumption on is previous games, but that is based on another coach, and things are different now.
So if Ruud stayed, he could have given Amorim some insider information, that way Amorim could have started a bit better. In any case, I am sure that we are going to see him do fine, he will need just a few games adjustment period, and if he can achieve that, rest will be much easier for him to get better results on. When you are a new coach, the hardest part is to get to learn more about players, and their personality, sometimes takes as much as months but after you do learn more about them, you end up not getting anything worse, you end up only growing better.