I had no idea that commanders who got "Lost in Time and Space" could come back (with more astral magic, but less sanity). I thought they were gone forever.
It would have helped if he'd come back to a province Rlyeh owned though.
So, I think the best plan may be to depend on bodyguards to overcome accidents at the void gate, but script returning so that when the Starspawn comes back from time and space, into a hostile province, he can follow the script and bail. Have to load up on pearls just in case the Starspawn chews through a bunch in the battle though.