Officially I would say when Sega dropped out of the console wars and sonic went multi-platform...thats when mascots died...Sonic VS Mario really was the whole mascot war...Sony tried with Crash, but it didn't sell systems.

I would disagree greatly about Master Chief or Kratos being mascots..the age of mascots are long gone. Halo will sell microsoft systems regardless if MC is in the game or not. Same with GoW.

But Nintendo announced that the WII U is launching with the All New Super Mario Brothers and it starred Mario & Luigi's cousins - Bob and Lorenzo then I don't think it would move any systems, or sell much. Face it..no one buys Sonic games to play only as Knuckles or Amy, they want to play as Sonic.