On the surface this sounds like bitcoin's PoW use will simply stop. It's actually the entire opposite.
When governments ban it, they go after sizeable, identifiable organizations running these operations, that is their only choice. These operations are optimized in their energy usage, because it's only in their interest to reduce their consumption relative to the value of the coin they mine.
The moment these operations are shutdown, there is a massive sink in the hash rate, smaller operations and hobbyists will rush in to fill it. Hash rate gradually climbs back up and instead you have 10x the energy usage because you can no longer run the PoW in a scalable way.