Obviously the transition away from oil should be gradual, and the sectors which are hardest to transition could be given more time to do so. But there's no fundamental need for large scale use of oil, it's just the current infrastructure and limited tech that's the problem.

Hundreds of millions will die due to climate change if we don't act.

I'm sure it would, but it could also be avoided without any major problems.

The problem I think, is that oil would still be mandatory because of competition between countries. Especially if there were wars.