First of all I don't make ethical decisions based on what-ifs. To answer your what-if, I would do all I could do. I presume it would not be too difficult to get custody of my own wife's baby. If not then I'd fight harder. Presuming he was still alive. And presuming his was still alive and tried to insinuate himself into my and my wife's life after raping and impregnating her it wouldn't last very long. His life that is.
Why not? I don't think insinuating oneself is a fatal condition. You certainly wouldn't kill him for that, would you? It isn't a valid reason to kill a person who is just an inconvenience.
Mind you, I'm on your side here. I don't think abortion is right in such cases. Just...well, curious.
As for "I don't make ethical decisions based on what-ifs," you ought to try it occasionally. Socrates (a notoriously inconvenient person) recommended it.