You can't undo what you've already done. You wouldn't have known that Lewis's actions could be counterproductive if I hadn't told you. Still, what he does will give them pause.
McCain would need to make five Persuade rolls, including the one he's already made, since that's how many civilians he can see. Even so, I don't think he's going to have enough time for Persuade to work before next round, so you might as well not bother. There would be time for Fast Talk, but that won't work on someone who's already been Persuaded by someone else.
The link to the original 2d6 roll of 6 damage is gone from your post now, but I remember it and I could always find it again later. You'll be happy to know that, combined with the 4 from your damage bonus, you've now done enough damage to take down the creature! Even if you hadn't, Mr. Foo had a good chance of finishing it.