If he stayed in the US he would've been thrown into a dark, black hole for all eternity to be tortured by the same types of sociopaths in the US gov't who committed atrocities like Abu Ghraib. I'll take being a Russian "asset" over the wrath of the US intelligence services any day of the week.
I doubt he could have been disappeared after all of the attention. Chelsea Manning wasn’t disappeared despite causing a similar black eye for the US government.
I’d argue he is more physical danger now being in a mafia state near an active war zone.
That said, I wouldn’t come back and subject myself the whims of this administration.