everything can still happen, even psg who is ahead of winning 2 away goals is still able to be beat by man.united in Paris, and at Camp Nou, the spirit of Man.united is still the same.
Of course anything can happen in the game of football but the PSG match is quite different to the Ajax and Manchester Utd match because PSG will be home while Ajax/Man Utd will be away and the possibility for the home team to win is higher than the visiting team.