There MAY be a few cases where alternatives are harder to find (where you need the chemistry of the gas rather than the energy), but that is a pretty small percentage overall.

But to produce energy at prices that are competitive to typical prices for NG is pretty hard without either coal or cost efficient nuclear, at least in colder climates. Solar is perhaps close to becoming cheaper in sunny, dry areas further south, but wind power looks like a poor alternative at the scale needed, since it's so unreliable. Maybe one day batteries or other storage will be cheap enough that we can store wind power for a week or more, but for now, it looks like the only low-CO2 option is nuclear.