If you see damage underneath the bumper, It is not that hard to remove the bumper cover.

If your car is like my '88 745 GLE -

There are small round rivet-like fasteners holding the bumper cover in place. Each has a pin in the middle - you need to push it through the rivet with a narrow pin. If you do this on a clean floor, you can probably save all the plastic pins after they have come out.

When you have pushed out all the center plastic pins, you can remove the rivets.

Then you can take the bumper cover off.

On my '88 the steel bolts had corroded the aluminum bumper to a gray paste and the bumper dropped a bit.

I cut out the bad areas and had a welding shop weld in patches, I drilled bolt holes and reinstalled the bumper.

The patches interfeared with some ribs inside the bumper cover, I cut out the offending areas with a chisel and reinstalled the cover

To put the rivets in place you just insert the pins into the rivet about 1/8th of an inch, when thr rivet is in place, push the pin in flush - this expands the rivet.

Except for the welding, this is at most two wrench (out of a difficulty scale of 5) job.

I was rear ended twice, low speed though and just bumper skin blemishes for me. The other vehicles suffered grille, radiator damage and bent hoods. My tail pipe got a little bent and that was all. Love those bumpers.

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

He has insurance I hope? Car prices are really high..demand as much as it takes to restore it & all rental fees covered.