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.
Manchester united understands that Van Niestelrooy is a very important piece in their coaching crew and he has proven beyond reasonable doubt of how much he's deserving of been maintained as their coach or even been in the crew to help and assist. Amorim in piloting the affairs of the team but Amorim is coming with his own crew according to the news i got and they may not be needing the presence of Nestelrooy and so Manchester united will have to let go of him.