I have to thank a friend for this, but there is yet another context clue for the protagonist that the timeline G'raha hailed from still exists: G'raha's memories of that timeline still exist. If the timeline had vanished, the aether that makes up G'raha's memories of that timeline would have poofed too. They didn't, as we'd know because we uh. . .inserted those memories into his younger body on the source?