I'm going to hold off on giving these governments credit until one of these bans actually goes into effect. Even the most aggressive of the measures that has passed still has a decade in which to be weakened, delayed, or reversed.
The decline will be rapid. Why maintain a fuel supply chain when there aren't many customers?
https://en.wikipedia.org/wiki/Phase-out_of_fossil_fuel_vehic...
Mercedes just announced that they will cease development of combustion engines to focus on EV's. VW Audi Group just said that this is their last generation of combustion engines. I suspect we'll see similar announcements from other manufacturers in not too long.
We may see some countries soften their goals, but I think if some of the big automotive players commit to having products available to meet those goals, there won't be much need to relax the goals. Only things that would cause a rollback is if anti-environmental politicians get into power or governments attempting to protect domestic car companies that are late making the shift.
Luckily renewable energy is getting to the point where it actually saves money over fossil fuel based energy. People might be loathe to move to electric or fuel cell vehicles, but costs are coming down there too, not to mention that many governments are banning ICE vehicles anyway. So the costs of shifting may not be that bad, and people will be able to realize some cost savings.
Right now we're at a point in history where shifting to a carbon neutral economy will be uncomfortable in some ways, but not horribly painful.
But the longer we wait, the more likely it is that we'll experience a lot of pain from climate change consequences. And the climate change will destroy a tremendous amount of wealth, cause massive refugee crises, and cause massive drops in food supplies. When those things happen it's going to much harder to make the shifts to clean energy because many will just be worried about surviving disruption in the short term.