Right now we don't have any idea what's beyond that door. It's just as likely that it's bad as it's good.

[Sorry, if you were expecting him to have all that deep Daitengu lore, he doesn't.]

It could be the way out of here, it could be sealing away the Daitengu's ancient nemesis that will destroy the town. It comes down to how you weigh the kind-of safety of Hirajiro right now, compared to the possibility of moving forward.

...I guess we could ask the Daitengu.