Avoid oncoming traffic and total damage is liable to who?

Our son is on a rather narrow road 3.95m after work. His side strip is 30 cm and then goes down the slope. Every 100 m there is a lantern pillar. He is already on the dike. Opposite track has at the beginning 40 cm, at accident height also 20 cm and on 2 m the earth is washed away – so nothing. Son (golf class 1.69 wide) drives already half on the dike, coming van of the 100000 Euro class (1.93m wide) drives only right and d moves over the middle line because his strip is getting narrower and narrower. My son who already drives with the tires on the roadside asks himself Van or lantern. Schlittert braked 5 m above the side strip and boing! As stood the road then still had 2.5 m. The van driver has 3 witnesses in the car (sister and wife) and thinks what he wants, he has three witnesses! Police call and two youths say from the van driver had driven over the middle. His insurance part he said that he was not aware of the accident and that nothing had happened to his car. 3 witnesses could confirm this. Police report is not yet available. Well, what do you think? Thank you very much for advice and information.