
I don't favor the notion, myself, but a set of dermal assault implants might go a long way towards explaining how the courier survived two shots to the head. Hell, technically you could even be the Chosen One- he's only 60 as of the start of the game.

you could even be a vault dweller or Enclave deserter, if that was up your alley. I think that's the charm of a blank slate character- the Courier can be anyone, within certain limitations. It's left in the air like that deliberately, so that it's up to you to decide what your character did with his/herself. Since he didn't know what became of the Chosen One, there's nothing that states that the Chosen One stayed behind and lived in New Arroyo until his/her death, or if like the Vault Dweller he/she went back out into the wastes at some point, lost to history. Marcus' description of what became of the Chosen One doesn't pinpoint when the two parted ways, but since he tagged along during the assault on the Oil Rig, it wouldn't be entirely unlikely that the parting was because of Marcus' personal dedication to his race, and his pilgrimage East which ended up in his founding of Jacobstown to try and research a cure for the Nightkin's schizophrenia. Since the Enclave Remnants that appeared in New Vegas was clearly elderly but still alive, it warrants the possibility that the Chosen One, too, is still alive. While the Chosen One's age could be a range of possibilities, it's safe to assume that he/she wasn't too much older or younger from the then-prime Enclave soldiers that they fought against.

It was obviously left open-ended because he/she was the faceless canvass for the player in FO2, so unlike NPC companions such as Marcus, there was no purpose in the Chosen One making an appearance elsewhere.
