[The harder Sans thinks about this, the more weird concepts start leaking into his mind. Stuff about timelines, and souls, and...magic? It doesn't feel as weird as it should, though. It just feels sort of sensible, and useful. Enough that, for the moment, he isn't separating it from present reality.]

Timeline discrepancies wouldn't exactly be unprecedented at this point - but hell if that doesn't open a whole new can of worms. Say that you go on to have this kid in your subjective future...

[Sans draws a straight line on his paper, for Greg to see. He makes a crudely drawn, baby shaped icon at the end of it.]

But then somehow you're taken out of the picture...

[He moves back along the line to somewhere in the middle, and draws another dot - and the draws an arrow indicating it forking off of the path.]

Then what becomes of that timeline? What happens to the kid? He's still born if he's here, obviously, but...

[He draws an arrow from the baby icon too, leading to a question mark.]

Talk about having your cake and eating it too.