Where's the paradox? Given that a person has already appeared out of nowhere - matter/energy has been created - I'd say that having someone with identical genetic make-up to them running around is minor stuff.
I exist in 2017. I go to 1978. I kill my other form before 2017 is reached. Therefore I cannot have traveled to 1978. What has occurred at each particualy moment is no longer consistent in a way that is clearly comprehensible by humans.
It's either perfectly consistent if you go minute by minute, or consistency goes out the window without any murder.
1978: Some matter and energy materializes. It appears to be a human being. Where did it come from? It's impossible to tell; it has no past as far as we're concerned.
1978: Oh my god, the mystery human has just killed another human. They look kind of alike, I guess.
1978: The mystery human is now in prison; its lack of citizenship or identity ("yeah, born in 1952 my ass, you're clearly at least 50 years old") does not prevent its incarceration.
2017: Nothing of note happens. Mystery human would be eligible for parole, if he hadn't died behind bars in 1996.
I think the last part is key: comprehensible to humans. I see the paradox but it’s a logical one not necessarily a physical one. I’m not even sure what time travel really means. Do you look at a river and think to capture it exactly as it was an hour ago? Would it really be the old river then? If you did capture it and add a few extra drops then set it in motion would there really be a problem? I’d posit that the past does not exist except as a mental construct to begin with. A “present moment” doesn’t even exist, how could you have a past moment to return to?
Actually, of interest Wikipedia seems to say that you wouldn't have to leave Earth at all (just bring the other half of the wormhole back), so I think you're right that it doesn't solve the grandfather paradox: https://en.wikipedia.org/wiki/Wormhole#Time_travel
But maybe when you go back you instantaneously become you? That would close the loop. The future you had essentially ceased to exist anyway so there's no reason to go back.