Fun time travel story, but if I take the ending at face value, inconsistent. Every attempt on his life before was prevented "magically" by intervention of some invisible force to prevent a paradox. So, there's some time daemon watching over and ensuring the sanctity of the timeline, I guess? Wouldn't that also mean that if he did manage to not have children, he would be causing a paradox. So the same time daemon's going to jump in and prevent that change as well--how is not exactly clear, maybe artificial insemination? Or love potion? Either that or his decision means nothing, and he ends up procreating anyway.
Either way, there will be more attempts on his life, despite his decision.