I briefly entertained that thought before dismissing it. But then again, who knows.We'll almost certainly see her in the next game and we'll have our answers. Or at least 1/4 of them.Perhaps the power to "bring back the dead" will come up later? Perhaps not literally, but as some sort of "illusion?"
In 3rd, Kevin's confirmed that the first statement in your spoilered section is possible.
Sora no Kiseki the 3rd Spoilers:
Salt Paling Memory Door- one of the reasons that Kevin made the weapon is because "resurrection becomes impossible."
So I've not discounted that.
I've also not 100% discounted any characters said to be dead.