Being a believer in God, and assertting "There is no sorrow Heaven cannot heal", a case like this requires some extra thinking.
I've got a range of scenarios.
Probably some angels were having a hard time holding their noses around Josh, even for the sake of the kids. Maybe there was a Wednesday morning meeting with Jesus, the three Nephites, twelve apostles, and the destroying angel, a sort of sixteen to one confrontation, with a solid case in favor of the destroying angel.
"If we leave the kids, they'll never be able to recover from all these horrible facts in a whole lifetime."
"Yeah, you've got a point. They have suffered their share already. They deserve a better chance."
The Destroying Angel got the nod.
Probably Susan Powell is happy to have the kids with her again, well, not as happy as if they had all gotten a better deal in life.