That's the story I was sort of expecting coming into the final season. Certainly, the Night King et al ultimately marching on Kings Landing. That's at least a thousand miles from Winterfell, with the Eyrie and Riverlands in between, so the death toll would have been staggering and quite the CGI spectacle. I like the way Winterfell plays out, although, I'm not sure how they get all the prime characters away. They'd need some sort of diversion or blockade to run like hell south and still put up a formidable army to knock on Cersei's door with. I like that the Valyrian steel isn't strong enough for the Night King, and something stronger needs to be manufactured. Something that would require cooling within the beating heart of Dany for instance. The weirwood source is pretty good, but destroying it is too terminal, as this is supposed to be a threat that can't be permanently vanquished, only silenced for a millennia or so. I guess that's not important for the TV show, though.
It probably makes a little more sense to swap Dany and Cersei's final dispositions. Dany, probably grew up lonely, timid, and scared. Removing people she's grown close to, would probably push her more toward sadness and hopelessness than the rage and bitterness as portrayed on the show. Whereas, Cersei grew up entitled and portrayed all the unpleasant qualities that come with entitlement. She actually knew her mother who she feels was taken from her by the little monster. She's had three children all cruelly taken from her. She was publicly shamed. She blew up the sept with hundreds of innocent and decent subjects. If any character is likely to go "mad", it would be her. Instead, she concedes the battle, cowers in tears at the end and only longs to be far removed with Jaime. One final attempt at making her a sympathetic character. I don't think so.