stannis would throw that bytch to the bushesidk. the north are VERY dedicated to the old gods. only the north is blood of the first men and have that history. maybe at first, before stannis gets the throne, if anybody in the north brought up being independent ned would squash it. but if stannis gets the throne, and just a year later is trying to convert ALL of westeros to the lord of light, we might have a jihad on our hands. there is no way that anybody will put up with that. if stannis is like "ok ill let u all rock with your religions" there is no way melisandre is putting up with that. her god is a jealous god and every other religion is demon shyt to her.
assuming stannis would have won the throne, i just cant see there being peace. not with melisandre by his side. ESPECIALLY if she helps him win the throne. she gonna be like "you owe me son "
that religion is only a means to an end, he doesnt give 2 shyts about it