if not managed to get the Europa League. It will also be difficult in La Liga because Barcelona is not completely safe yet. Madrid is very close, and it won't be easy for Barca.
if the Europa League is too difficult for Barca later, hopefully, Barca can focus on La Liga, that's all that can prove the current performance of the squad. Likewise with Xavi's proof. though fans can see how much change Xavi has brought to the team. without trophies, you will not be praised.
But from what I can see from the players' performance in the world cup and the team's situation during this season, I can say the truth even if I can a fan of Manchester united I think Barcelona got a better chance because Xavi can give a better atmosphere to his team and can make them a better situation also his a champion for his club but there not a such situation on the other side of the story for Manchester united. Yet nothing is clear to me but I guess this season Barcelona will win the cup.