My mother had an acciident as a mamed driver on my car

We are expecting her car to be a write off

Bit confused. Was it your car or your mothers car?

My car, but referred to her car as she was driving.

There are other details I don't understand ("hit from the passenger side at about 3/4 of going forwards"), but this was clearly a fairly major collision and whether the car in question is a write-off or not, a considerable amount of money will be involved.

Therefore let the insurance companies deal with it. If it had been something minor, paying for the other driver's damage and avoiding an insurance claim might make sense - assuming your mother was at fault (which is not clear).

Ignore the other driver. Was he in fact insured anyway?

imagine 2 cars aiming for the same point diagonally. so the car further back hits the passenge door and ends up in the front wing,

Absolutely, leave it to the insurance and block the guy. This happened to me once (disagreement on which lane to use at a roundabout) and we were perfectly civil with each other. I never even found out the other guy's name, much less his phone number, and it was all settled by insurers within a week.

I suspect the other driver has a problem with his insurance.