It would be hilarious for a Killer!Sans who left/escaped Nightmare!Sans to enter the Anti-Void and find Error!Sans, before Reaper!Sans could like in the Recall!Error comic.
Since Error specified before that he prefers Killer over Reaper, which got Anti using Reaper's form jealous. Also, Killer would be in his Sans persona, where his soul would resemble one of a monster soul.
What do you think it would happen of those two meet? Would Error attack them, or maybe Extinction, or do you think they would get along or even more?
Recall!Error didnt actually mean what he said, it was some kind of diversion so that he'll be stopped with being teased about Reaper.
Things would be the same as what Recall did to Anti when the latter first appeared in his anti-void. Attack and protect smol, pretty much he'll get rid of Killer on sight since he knew what kills is capable of and he's a nightmare henchman and Recall doesnt really like anything that has something to do with Nightmare.
BUT. But in such case that he would deem killer a non-threat, he'll probably let the other hang around. For most part, i think killer and extinction would have the most interaction('cause Ex would be curious why they'd kinda look alike).
they would get along but in a quiet distance, doesnt mean Ex would let Killer be any near of a possible lover to his mama tho so i dont think there'll be a error/killer, ex would make sure to not let that happen