In the scene where the road accident is shown, we see that it was a T-bone collision, with the other vehicle impacting the driver's side of the Stone's car.
We're not specifically told this, but it can reasonably be inferred that at least part of the reason Vic survived while his mother, Elinore, did not is because he was sat on the other side of the car, in the passenger seat, where the force of the impact would've been a bit less severe. Had Vic's father, Silas, been there, and in the driver's seat himself, he would've been the one to take the worst of the impact, while Elinore likely would've been sat in the passenger seat, increasing her chances of survival.
There are other possible explanations. Just before the collision occurred, Elinore took her eyes off the road while trying to console Vic about his father's absence. Had Silas been there, that specific conversation never would've happened, and as such, the collision might've been avoided. Also, had Silas been there, they might've left the football stadium a little earlier, or a little later, which in itself could've prevented the collision.