People have been dying while playing video games for decades. Back in the 1980s there was a huge "scandal" (quotes are very necessary here) when a teenager suddenly died playing in an arcade. I think he was playing "Tempest" (an old cool vector graphics game). He just went PooF! The headlines ran "TEEN KILLED BY VIDEO GAME!" and a whole slew of concerned parents formed support groups and went nuts about the relatively new "deadly" technology. After a month or so of this, it was revealed that the poor guy had had a heart condition, and it just happened to trigger while he was playing. It was a sad story on many levels.
But repeatedly playing for 10-12 hours straight can't be good for a person. I can't imagine it. No game is THAT great. But it's hard to believe that gaming alone could actually kill a person.