Best theory yet.
You shouldn’t need much of a plan for an endead army. The established rules (fire, obsidian, Valyrian steel) make them a little less indesctructible. If the corpses in “the crypt” are able to get out of their individual vaults, though... That’s sort of another Deus ex machina. This story is so full of them lol.
I don’t expect Ser Brienne to die, but the rest of the bottom row...