That survival half-life thing was postulated by Steve Young and Dick Bueshel and a couple other prominent people in the hobby in the 80s. It's backed by -zero- evidence. Through the decades since it just keeps getting repeated as gospel. The short answer is that no one can actually answer this question.

Same as everyone says there's no such thing as operator raids anymore, that's they're all gone. Until the next big one comes up, like the one in europe a couple years ago that yielded a bunch of great condition 50's games, stored nicely throughout the years until the operator passed and his family started to explore what was there.