In the book, during the fight with the boy, the wife dies. He's upset, obviously, and starts to think... what if it was because I took so long to put him up there? She's right here, so maybe if I go now... And he does, and buries her. He hears her come in the door behind him later, and she lays a hand on his shoulder and says 'Darling...'. So, his supposition was correct to at least a point; his son had no speech if I remember correctly. Soooo, it could be she was OK and just alive again, or she was possessed by whatever it is that indwells in people buried there and it was just stronger.. who knows?