I think you got a solid idea of what's up here but I don't think Rasputin took out humanity seems to be to much alien activity around us in the aftermath plus I think the "darkness" is a opposite of the traveler seems fitting seeing how the traveler has been crippled/ dying such a being probably needs a very powerful foe seeing how it still some how protects the city/ tower of the last humans. Does he have a shield over us?