i think Dollar could still subrogate any damage to you... perhaps even if you had not signed any documents with them. If Dollar had you sign the releases before sending you to Enterprise, the subrogation would be fairly straightforward. If they did not have you sign anything, they might have to sue you in order to collect damages (and the degree of difficulty in collecting would vary by state / locality in which the loss occurred). Of course, its all moot since you returned the vehicle intact.