There's simply no way that Sansa says "Sorry the North is going to be it's own sovereign land" and none of the other leaders don't chime in and say "We want independence as well". Heck it probably would have made more sense for ALL of the kingdoms to be governed independently. The Iron Islands have literally fought to be their own kingdom but when presented with a chance to actually have it happen they say "Nah we're good, we'll just keep reporting to King's Landing". Stupid. And it was totally the reason they had Sansa speak last. Otherwise I imagine all the other leaders would have said "Oh wait that's an option, then we vote to be independent as well". Just another area where the writers did the bare minimum.