Full refund- if they just pay for a new frame-it will cost more than you paid for the bike.
All your money back-shipping+ actual buying price.You give up the entire bike.

It is aluminum right? Nasty dent, and aluminum isn't forgiving-steel slightly more forgiving

.Now real life, if I had dented the bike, and was stuck with it-I would ride it, and not worry about it. Now I would probably look for a donor frame, so switch parts over, but if it was my only bike-darned right I would ride it. This is strictly me, I take chances. Of course it is MUCH MORE LIKELY to fail than an undamaged frame, but it probably will never fail.How likely to suddenly fail, and drop you in a tumbling mess on the road/trail- NO ONE CAN PREDICT THAT?? Maybe the manufacturer has numbers on failures, but they sure won't let you in on it.

Get all your money back-forget about a new frame(maybe, maybe you can suggest you would like to buy it as salvage, but that is kinda tricky.
Charlie