Now Sam only kills himself, no one else; Tim Price' idea of not coping with his reality and escaping to Narnia involves not just his own death but his wife's and child's, but isn't the emotional reasoning at least a tad related?

Yes! I thought the exact same thing, except I have no idea how the Gene/Aslan thing comes into it because Gene wasn't sacrificed/killed/whatever. It was Caroline Price who mocked him using words similar to that of the Witch, but it turned out she wasn't the evil parent. So yes, Narnia upside-down, perhaps. Alex has her child binding her to the "real" world, so maybe unlike Sam she'll go back.