Vincent was dead from Butch shooting him, Jules had quit and gone to wander the world, and Winston Wolf wasnt exactly an avenger type guy, just a cleaner upper guy.

So there would no consequences for Butch if he just left the pawn shop and stole Zed's motorcycle and allowed Marsellus Wallace to be raped and murdered, even if Marsellus told Zed and Maynard what Butch's name was he was going to leave town soon anyway, Mr. Wallace doesnt seem like a snitch though, even if they told him that Butch was gone and had escaped.

So Marsellus Wallace would have been killed shortly after Butch escaped anyway, no more problems with him and it ties up things nicely, also rids the world of a scumbag gangster too, Butch was already trying to kill Marsellus himself twice anyway, this forces Zed and Maynard to do the murder and dispose of the body, good times for them unless Marsellus Wallace escaped from their grasp and fought back.

On the other hand Butch could have just called the police and reported what happened and said that a Black man was being raped in the basement of that pawn shop by two Rednecks, describe the crash and omit his name, let the police be notified and show up to arrest Zed and Maynard and Marsellus Wallace, all three would go to jail and a lot of explaining would have to be done.

Marsellus Wallace might even lose his reputation and street cred after being arrested because the police would sell the story to Inside Addition or Extra or the Tabloids, not something Marsellus Wallace would want to become widely known and now it would be huge news.

Just my thoughts.