Fuck ... I'm so sad. Even if they passed away without their souls being stuck in eternity with that bitchass evil god, the fact that they still passed away relatively early in Will's life just sucks monkey balls. Imagine your mother and dad, the only two (besides the gramps) you had for 15 years with no other single relationship, then they're now gone just like that. Imagine if your parents were one of the only people you knew, and on top of that they were one of the best parents you could have asked for, and you lose both of them in a single night at age 15. I don't think I'd be able to get over that ever.
And goddammit, author is making this even doubly more sad by showing Blood and Mary's backstory ... fuckin hell