I don't think any particular game will be the nail in the coffin - if Bungie keep making unbelievably stupid decisions (no content for a whole year - how did you think that was going to pan out?) the player base will slowly and quietly continue to shrink until somebody high up at Activision makes the call to pull the plug. To play on a famous quote that Bungie once used while at the absolute pinnacle of their game making: "This is the way the game ends...not with a bang, but a whimper"