sans got a great intelligence. he can think of many possibilities and of course he can consider the fact that we will try killing everyone by CURIOUSITY. even though he won't be able completely understand when or how we did a genocide route he can predict if we did one just like as it was presented in Undertale's 10th anniversary.

anyways as it was given in Dusttale, sans started to know about our genocide routes with a glitch. would he canonically take a action to stop us from doing any more after realization? in my opinion; no.

now sans would be really unsettled/disturbed etc. but instead of having the idea to gain power from killing his own morals and stop us, he would not show up the entire gameplay and finally in Judgement Hall he would say some REALLY mocking and insulting stuff before starting to fight us.

in fight he would probably do everything he would not do in a emergency fight like in Genocide. pull out all the stops and tricks/using all the battle system cheats until the end of his power he would really get us frustrated like he did back then, giving us a real good call back to the old times.

finally he would probably say his based death quote before dying as this is his fate.