I reread Rockslide and Summoner's game in x-men 11 and 12. I'm not convinced the corruption thing was because of otherworld. While it makes a nice mechanism to up the stakes, I think they might lose someone and think they are gone but when the revival happens, they come back fine.
The game was all about finding weakness and knowing your opponent. Summoner mentions how he knows Rockslide and his memories. And how the game can make you lose everything. Summoner even mentions that the fame taught him how to kill Rockslide. And none of the council or five (bar Apocalypse maybe) know about the game. They wouldn't know to account for that.
Could also be a nice fake-out on the death, having rockslide come back once Summoner gets whats coming to him.