Obviously Square doesn't think that this is a very big deal that requires a lot of explaination. Their tone was almost like "common sense! duh! of course she'll come back!!" so i don't think they expect all this depth of explanation.

i think aeris is sort of like Maester Mika and Auron. She died peacefully and can come back but she stays in the lifestream to tend the planet or something. Hmm, if she really is like Auron, then she's kind of selfish to leave everyone grieving over her when she can just come and go.

I'm confusing myself pretend i didn't say a thing