I am sorry to inform you your son has died of dihydrogen monoxide overdose, we will need to heat him to a high degree to remove the chemical. He will be returned in a silicon dioxide container.

yes

voila: https://hollowknight.fandom.com/wiki/White_Palace#Points_of_Interest

as long as the cutscene is not watched or game isn't saved, PoP can be re-entered, but not redone