Council of Elrond

Each character in the company faces one strike. After the attack, the defender must reveal one random card from his hand for each character in the defending company.

Would "after the attack" resolve, if the attack was cancelled?

Yes. Attacks that are cancelled are still considered to be “faced.”

Now, if I had an ally in the company attacked by Crebain, the ally would need to face a strike, but he wouldn't be considered a character for the purpose of the "After the attack" action, correct?

Correct. So far as I know, there are 2 separate conditions taking place:

The first is that “each character faces one strike” and allies count as characters for the purposes of combat.

The second is that “defender must reveal one card for each character in the company.”

For the latter, you are just counting actual characters in the company. This condition is independent from the first.

If I am mistaken, I will rely on one of our designated Rules Wizards to correct me. =)