No need to get into climate change. The externality of pollution alone is much greater than any subsidy. Natural gas wouldn’t go bankrupt and it’s necessary to have natural gas peaker plants when you have renewables.
But we should look at each fuel individually. According to one study, air pollution costs of coal are 32 cents/kWh, 13 cents/kWh for oil, and 2 cents/kWh for natural gas. Other studies have come up with lower amounts.
https://www.ucsusa.org/resources/hidden-costs-fossil-fuels
In this report they state that the cost of fossil fuels is 2.9 trillion in the US alone (this number is higher than the IRENA report and some other analyses). https://energyandcleanair.org/wp/wp-content/uploads/2020/02/...
But we should look at each fuel individually. According to one study, air pollution costs of coal are 32 cents/kWh, 13 cents/kWh for oil, and 2 cents/kWh for natural gas. Other studies have come up with lower amounts. https://www.ucsusa.org/resources/hidden-costs-fossil-fuels