I'd say a good chunk of them, but hopefully at the same time other gas stations are being decommissioned and replaced with sustainable generation.
If I look at NZ then in the last ten years pretty much all coal generation has moved to gas but in the same period about the same amount of gas generation was decommissioned and replaced with wind with thousand more MW of generation from wind and tidal consented to be built.
Natural gas is likely as bad or in some cases worse than coal from a climate change perspective (mostly due to pipeline leaks and leaks at the fracking sites). Switching from coal to nat gas may be better for air pollution deaths, but it's just as bad for climate change.
The article I read in NZ showed that natural gas had about half the emissions of coal overall. New Zealand is very seismically active so there's a lot of gas and most probably it's close to the generators. The intention is to move from coal to gas to tide the country over until it can be replaced by wind and tidal. The goal was recently raised from 90 - 95% renewable generation by 2025. Right now on average it sits at 83% renewable but in summer when electricity usage is lower it can be more than 90%.
It's roughly half as bad as coal nominally, as in when combusted. It's when you look at the whole system, including pipeline leaks and fracking-site leaks that it starts getting bad. So changing infrastructure from coal to gas is approximately worthless from a climate change perspective.
Certainly an improvement but it's not like we're replacing them all with renewables or nuclear.