Missing a party regardless of what the party was for, is not grounds for a lawsuit. You can of course recover the cost for damage to your vehicle and medical expenses (if any) if the other driver is proved to be the one responsible for the accident. Unlikely. For damages to be compensatable, they basically have to be of the type that are measurable. I suspect that missing a good time won't qualify in the eyes of the Court! Essentially, the at fault party has to restore you to where you were before the accident. You hadn't mssed the party at that point. You can say, that the event, like all others, may change the course of your life, doesn't make them responsibile for what happens in your life. If while missing the party you purchased the ticket that won the zillion dollar lotto, you wouldn't owe them either.