Butters' death was faked to get hold of the girls' "future telling device" at Heidi Turner's slumber party and ran off with it. It is unknown whether the girls realized at that point that Marjorine was really Butters as after that, the girls just said "What the hell?" and "Someone give me a piece of notebook paper so I can make another one."
Marjorine's mother (which was really just Cartman) made sure Butters went to the party and the other boys kept watch outside the Turner Residence.
Cartman was Marjorine's fake mother, claiming "she" is a governer's assistant. For Marjorine's real family, see Butters Stotch.