If he can get the team out of that state I think he will have no problem maintaining those very improvements in the team's stats, so it's too early to say he won't succeed, but I agree that Nistelrooy shouldn't have been sacked, he really knew the team well and at the very least could have pointed out to the new head coach the team's mistakes that should be corrected in the first place
The fact here is that he needs time, he is just arriving at the club, which he knows nothing about, starting from the kind of quality of players at his disposal, the pattern that suits them the most and I believe that it's definitely going to take a whole lot of time for him to realize and knows the strength of his players.
And yes, it's true that rud van nistelrooy should have been retained at the club at least till the end of the season to know if he can lead the team going into the future, but as it is now, the deed has already been done, their is no need of crying over a spilt milk, so all the Manchester united fan should just be patient and get behind Amorin because I believe that he has a whole lot to offer this team, what he definitely needs is time to implement his playing system across to the minds of his Manchester united player, because he is definitely going to deliver more than what Eric ten hang did at Manchester united, am very much certain on that.