The worst possible option: As soon as the player leaves the Nowhere Mall that entity we see after backtracking through the White Complex entrance in the decayed version comes in and kills her.

Best possible option: Inno 'leaves' the Nowhere Mall and becomes a wandering entity like what Jimmy and James seem to be. After, that same entity I mentioned before moves in and the place quickly decays to the point we see it in when returning.

I haven't checked out the other maps yet. But if she is a "sunfollower", in the map the sun is now setting. So maybe she followed it away from the mall?

Question: Has anyone managed to open the apartment door?
(The same one we started in if we entered Void Mall)

https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=3543408744

In terms of lore, there's nothing written but the scraps found in the maps.

I'd say it's simply what the mall would look like if Inno wasn't there, since she's kind of the handler of the place.

If you want a more grim view, take it as that she got completely consumed by the Pink Star and turned into something we might never be ready to see, but that's just my take on it