Santino D'Antonio arrived at John Wick's house to ask if he could aid him with killing his sister Gianna D'Antonio so that he could take her place. John refuses angering D'Antonio who then fires a grenade launcher at his house destroying.
John then decided to kill Gianna anyway due to his blood marker. He then hunts and kills Santino in the Continental Hotel while Winston watches.
After Santino is killed it is unknown what happens to the Mob. It had either fallen apart or another possible family member started running it like Abram Tarasov.