Question about Marty disappearing.

So, if Marty didn't succeed in getting his parents back together, he would’ve been erased from existence.

Then what? Does Doc still go on inventing the DeLorean? Would Lorraine just not marry George? Would she marry Biff or someone else instead?

If Lorraine ends up marrying George because they bond over Calvin's mysterious disappearance, would Marty reappear in 1955?

Would the solar system/universe just get destroyed?