I think Erina ascended and Shirone just met her. She wasn't a mage but her insight was good enough that you could call her omnipotent. Giving her alpheas' memories probably gave her omniscience as well. I'll bet that she was put into a similar state as Shirone, and the reason she was so sure he wouldn't make it back is because she failed to. Meanwhile, Shiron ascended and managed to return. Possibly because he's the perfected fusion of the both of their memories.