Just saying, he had a damn shotgun pointed right at his face after escaping the warehouse, he could have prevented the death of Marcus.
shareHe thought that would be the end of it, and he didn't know Viggo was going to attack Marcus. In fact Viggo wasn't going to attack Marcus, until he later found out Marcus had been helping Wick which resulted in the death of his son.
shareAnother good question would have been why didn't he kill Perkins. She tried to kill him and obviously was going to try again if she got the chance (I imagine that's why he asked Henry to keep an eye on her).
shareNo killing allowed in that hotel
shareHe didn't kill Perkins because he assumed that he was a just a "job" to her. When he forced Viggo to pull the contract there would be nothing in it for her to want to continue trying to kill him.
shareHis beef was with his son. Not viggo. Wick is a man of targets. Viggo wasn't the target. His son and crew was.
shareA better question would be why didnt Viggo kill wick when he got the chance?
He went for the traditional James Bond Elaborate-death-mechanism while walking away assuming it went fine , as illustrated so eloquently in Austin Powers