The fact is that the team that has not have the ability to win against Benfica. We should not expect such a team to win against Bayern Munich. Yet it is a football match, anything can happen on the field. But if Bayern play with their full strength, and if they really want to win this match, Barcelona will lose.
In fact, it's huge luck that Barca has any chance at all of advancing in the CL. If you look at the last game against Benfica, Seferovic of Benfica had a 100% chance to make it 2-1 for Benfica in the last minute of the game. He missed miserably. If he had made the goal, Benfica would already be as good as further and Barca only in the Euro Leauge.
Bayern is a bit weakened at the moment and they have the league top match against Dortmund on Saturday. I see that as the only chance for Barca.