Van Gaal already knew he will be sacked before the FA final, he lost his job after the lost to West Ham about 2 weeks ago which kicked Man U out of the top 4.
I remember during preseason Ed Woodward set the season goal at top 4 finish / Champions League spot, which is a clause set by Adidas in the billion dollar kit deal. Van Gaal agreed to Woodward's season goal and even set his own target at top 3 finish. Van Gaal knew he would be sacked if he fail to finish top 4.
I like Van Gaal but it was boring to watch Man U play football for much of this season, there were few shots at goal as they had difficulty creating and scoring, and their defence was terrible. Fortunately their youth players Rashford and Lingard scored some crucial goals to rescue them from disaster. Martial is a good buy and probably their best player now along with David de Gea.
Wonder if Mourinho can make the team attack and defend much better, if not it will be another boring and awful Man U to watch next season.