Death of mother in road accident

My mother died on the spot in a road accident. My sis was with her at that moment. They were coming out of a banquet from a b'day party. The driver of the car was held on the spot by my sis and my cousin ( who was talking over phone outside the banquet at that moment). My cousin became the first eye witness . Since sis was not in a position to talk at that moment so she gave her witness very next day and thus registered as second eye witness.

Opposite party i.e. the driver had clearly denied the fact that he has done anything wrong instead he said I stopped my car just to help them out. Now my question is , What if my cousin doesn't appear on the date of hearing for his witness? To what extent it can affect the case? Will there be any compensation by court under such situation? My sis evidence has already been done on the last date of hearing & Postmortem report also states that It was death due severe injuries caused in an accident.