In any way, I would also take into strong consideration that the truck will never be the same truck ever again after being involved in a crash..
It might be fixed, working fine and all. But still it will never have the same value, and issues WILL come sneaking in on it later on. Be sure of it!
This really is a mess.. At first I thought you borrowed the $6500 to buy this truck, if that was the case "I" would have told my "friend" to come pick up the rest of it and call it the day.
But since this is not how this went down from the beginning, I would strongly advice you to go talk to a lawyer about this. Get the story straight first, so everything gets on the table.
You might have to pay back the $6500, but I also think you might have some rights to claim some $$$ back for the loss of your truck..