define who's not mine.
If you mean the rape thing you can do to NPCs treat it like she's stunned. I do use the rape when she's sleeping I just dont insert it the hit function can be clunky I rarely rape NPCs because I dont want them to have a -10 on me
I think they mean to say "does it make sense to impregnate an NPC that does not belong to my faction?"
But to answer the question myself, no, individual enemy NPCs despawn and no longer exist when outside a specific radius of you, so, impregnating them would make no difference.
However, if you were to impregnate them and then capture them for your own faction immediately afterwards then the pregnancy 'should' carry over.
The enemy NPCs do not get up again after being downed unless you convert them anyway.