But can he really be an alternate father if he was never to be a father at all?
Prior to your muder of him, he's just an alternate version of the man who is your father, not actually an alternate father. Atleast, that's how I'm seeing it.
If you kill a guy who was going to be your father, he never was going to be your father even if he's from an alternate parallel universe, surely?
But anyway, someone should bring up another paradox/impossible situation.