Aaron survives, though his doppelganger does not! He'll come back to Earth and use his fake identity as Nathan Camlost to be part of disaster relief efforts. He'll be around, here and there, though I won't be playing him in RtE.

His STE CR is completely free to assume he's around and still in touch; he'll keep his Echoes, if that's allowed. Even if he loses them, he'll stay in contact with the people he met through the Numbers, as much as he can. You're also totally free to handwave him helping you out, if you need him.