I've got the opportunity to buy a cheap 2017 A200 that the insurance has written off. It's a distance sale, so I cant see the car until I buy it. As far as I know, the car was running fine before the bump. it has only done 40,000 miles.
External damage is minor, but it has a gearbox fault. I've done some google research, but cant really find much info on this. There are a couple of posts about following the on screen prompts, pressing the SOS button and clearing other faults.
I usually work on BMW, so have little knowledge on Mercs.

So my question is..
1. How bad 'could' this be. Is it very likely a software/calibration issue. Or could it be a serious mechanical fault the needs a new gearbox.

 

From the looks of that, the wheel took the brunt of the force. So there is a good chance that there is some damage to the transmission, from the force of the axle being pushed into the tranny. If you or someone aren't able to get under there and have a look, IMHO you are taking a big risk.