The second group of girls appease Jasper by trading in Mike's car.
Think about it. With Mike dead, the girls now have in their possession a 100% reinforced death-proof car. In short, it's probably worth quite a bit—beat-up or not. So they bury Mike mafia-style, drive the car to Jasper, hand the keys over to him, make it an effective trade-in, and head off with the Vanishing Point car. Fridge Brilliance, really.
Oh—and they pick up Lee, of course....
Except Mike's Charger got flipped by the Challenger that the front wheels are literally folded inward and one of the back tire's was completely ripped off, making it impossible to drive the car back. Not to mention, just because Mike made the interior death proof doesn't necessarily mean the rest of the car is (and with the way the engine compartment is crushed, it's safe to say that the engine is shot). The Challenger's damage is much less than Mike's Charger, meaning it would cost more to restore it to even be road worthy.
There is one other obvious problem: their chase and beat-down of Mike took place in broad daylight. The former happened in front of multiple witnesses, one of whom was bound to have a cell phone or radio, call the police and report the descriptions of the cars and the occupants. There wouldn't be any time to bury him. Plus, the Challenger sticks out like a sore thumb; the police would spot it. Other than Lee, the three are likely in a lot of legal trouble. Had they instead called the police and not gone after him, Stuntman Mike would likely be arrested and imprisoned. Especially when a background check brings up what he did in Texas. Then again, wouldn't have our satisfying final act.
