Okay, so lets say Lehmann doesn't get sent off. Let's say he does stop the other goals Barca scores. Now let's say that Arsenal doesn't get that terrible foul call that led to their goal. It's still 1-0. Lehmann wouldn't have been able to stop the shot from Eto'o anyways, so it would have been 2-0. He might not have been able to stop Belletti's goal in the 81st minute.
Anyway you script it, Barcelona would have won.