There's no going back to coal courtesy of the EPA
The EPA has pretty much shut down any new coal plants with new regulations on carbon emissions that coal can't meet. I don't know what the regulations are if a coal plant has been mothballed and then restarted, but the costs of keeping a coal plant mothballed but in a operational state will mean that most of them will be decommissioned if a natural gas plant has been built to take over for them.
Here in Colorado, for example, the state passed a law a couple of years ago "forcing" the power utility Xcel to shut down it's oldest coal plants and replace them with natural gas. This bill had the full support of Xcel, which saw it as a way to get state support for charging ratepayers the capital costs of shutting down old inefficient coal plants and replacing them with bright shiny new natural gas ones. In the long run this should result in cheaper energy costs, but to get there ratepayers have to foot the costs of building new plants.
