Question

What will happen when if all coal and petroleum are depleted?

Answer 1

it would lead to a very severe condition

Answer 2

There will be wars until everyone realizes that all these resources will be gone forever. Then, there will be panic. Society relies on these resources for power and mobility. Society breaks down without power, and we are doing every little thing we can, including pushing reactors to max capacity. Power is iffy but will be restored in a matter of months. No more oil, no more planes, cars, tanks or anything else that uses gas. That is, unless it’s electric. We will probably fully transition to electric motorways.

So, there will be a period of chaos, but then everything should smooth out in a matter of years.