If your rear bumper is still sitting level, looks straight and as square to the rear as before where you can't push either side in or pull it out no matter how hard you try then you may be good to go. In some rear ends the spring inside the two crash absorbers can be damaged and the shock absorber would need replacement. Take a look underneath and you may see evidence of how far the shock absorbers were pushed in. Shouldn't be too much from a wrecker. If you look in from behind with a good light you should be able to tell if the bumper itself is notably bent, in which case it would have lost structural strength and should be replaced. If damage to the bumper skin is mostly cosmetic then it can often by minimized with a heat gun, blade and then spray bumper paint (make sure to do a good prep).
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now