The way Strelitzia appears before Elrena and her Chirity is like an hologram or a glitch inside a computer. Not to mention both Luxu and Brain using the term "virus" to talk about something threatening the Master's plan. Do you believe the place where everyone is right now is actually a "virtual reality"? You know, like a datascape, like the one from Coded? That would explain how Ventus and the others survived for so much time.

Yes, this was basically confirmed to be a datascape. It's why Maleficent couldn't change her fate when she traveled back in time (and somehow wound up in the datascape), and it explains why worlds like Enchanted Dominion are appearing despite not being a part of KHX. (From a mostly gameplay perspective, it also explains the data Organization members, and it explains PVP from a partially gameplay/partially story perspective.)