Right now Marcus Rashford is not doing anything good like his didn't even make any sense in Barca jersey, and because of this Hansi Flick warned him that if he didn't improve his performance level then he would be sent to the bench for the rest of the season. Barcelona signed him to boost team performance, but unfortunately Marcus Rashford has not shown any improvement. So maybe Barcelona will just keep him until the loan ends and then send him back to Manchester United.
Marcus Rashford needs to improve his performance because Barcelona wants a player who can contribute to the team in a better way, and if he doesn't complete this criterion, they will kick him out of the team.
Rashford seems to have lost confidence since leaving Manchester United. He actually played quite well at Aston Villa, and I think he needs some time to adapt to the team and La Liga culture. Hansi Flick is a very experienced manager and can certainly help Rashford rediscover his best form. However, if he fails to live up to expectations in the first half of the season, it's possible Barcelona will return him earlier than agreed.
Rashford didn't do anything while he was on loan at Aston Villa because if he performed well the club would have made a move to sign him. He has long lost his confidence when he was still at Manchester United and it seems everything he is trying to do now to gain back his influence is not really working for him anymore and i don't even see him improving any time soon so it's obvious that Barcelona will return him back to Manchester United. During the preseason games when he made quite some good performance, people were already saying that he will be a player to look out for in the La Liga but it's been 3 games already and he has done absolutely nothing.