He is like a waste in the club and he is a selfish player. It was only last two seasons that he played impressively but after that time, he dropped form drastically because he isn't a serious person. United put their hope on the wrong players for transformation of the club and that's why they faced all these drawbacks. They should have sold him since but Ten Hag don't know what he is doing.
Rashford will not be included in the long-term plans of the team formed by Amorim. There are already rumors that the club management already has several names that can replace him.
I don't think it would be a problem if Rashford left United and tried his luck to improve his performance at another club. Reportedly PSG is also interested in him, but that news may just be an assumption from the media.
He will be considered a selfish player by most people by looking at his performances, but we never know the coach's plans in advance and I think Rashford is still a great player despite his decline in form.
Will he leave Man United? Naturally, the new coach has good plans for the future of the club and is more concerned with which players are suitable for him, maybe Rashford will leave but like him not in the near future or next summer.