Considering Toby's previous work, I don't think that'll happen if you go the violent route. Toby has never shy'd away from pointing out how much of an asshole you're being for killing the character's in his games.
My thought's for the culmination of a potential "genocide route" are Noelle goes completely off the deep end and decides to kill everyone (by freezing the world or something), maybe even trying to directly kill Ralsei or Lancer in the process. This leads to Susie and Kris (who would "override" any attempts at siding with Noelle) being forced to put her down before she kills everything. The death scene would also be notably brutal just to hammer in how twisted the route was and most of the characters are notably gloomier for the rest of the game.
Though that's just a surface level guess, Toby might have something "more" planned for any potential conclusion for the characters, but I wouldn't be surprised if he was shooting for something along those lines.
