their first match was a great win which ensured them to enter the semi-finals. However, Dortmund may not be able to win in the next match, Barcelona will attack even more strongly in the next match and enter the semi-finals, besides, Barcelona has the possibility of entering the final.
Sure, you know the first leg is always more important than the second leg and now that barcelona have succeeded in wining them with 4 goals. The possibility for them to win back with this goal margin is something anyone can not think nor imagine that it will happen due to how consistant barcelona is towards chasing this champions league title, so I don't think if there's still a hope for dortmund.
Many teams have taken the advantage of the first leg to secure victory to win the second leg, because they use the first leg to scored goals to beat their opponent to stand in a chance to win the second leg game. It will be difficult for Dortmund to recover the 4 goals from their second leg no matter the mistakes may occur in their second leg,because Barcelona will maintain that chance to secure victory in the second leg.
I know that anything can happen in a football competition, but I don't think Dortmund will equaliz this goals and still win Barcelona will not allow Dortmund to beat them, because Barcelona are very strong in this season to prove their seriousness in la Liga league and UEFA champions league, which people have seen and believe in their mission to lift trophies this season.