I have absolutely no skin in this game, but I am curious about the whole "mistake" fare angle. In years past, this was pretty cut and dry - $5 airfares were clearly an error. These days, though, with flash sales and twitter deals and whatever, there are extreme low prices available for limited periods; I know US had some insane twitter deals a year or two ago that were legitimate. My question / point is, how can UA or anyone these days prove that a fare was an honest mistake and not a flash sale that got out of hand?
Switching gears, I think the fact that some people have already travelled on these fares makes it harder for UA to regain control of the situation.