Power walls are pretty expensive. Much cheaper-- if you're primary concern is keep heat going and maybe a few other basics-- would be a low-maintenance dual fuel generator. Unlike the powerwall it's run-time isn't limited. Prolonged blackouts will run the powerwall dry, but with a dual fuel generator as long as you can get gasoline or propane you're good to go.

I suppose if you can afford it, go for both and have multiple reduncancy.