This happens to me a lot, Pope excommunicates a faction, I declare a crusade on offending faction, by the time I get there, sometimes only a couple of moves after the declaration by the Pope, the offenders have made nicey nicey with the Pope. One time I was one province away and getting ready to strike the excommunicated Italians. I was in a German province with my crusaders and I get the message that the target province has been returned into christian hands, your crusade has been disbanded. The next turn I get another message that the Germans will be glad to ransom back my army and level 7 general for 3000 florins. Nice con lol.

------------------
Diplomacy is the art of telling someone to go to hell so that they look forward to making the trip.