Well.
There are dogs roaming around the Buryakovka nuclear waste storage facility. About ~10 years ago I have been told that their average lifespan was in a ballpark of three years. Make what you will from it.
OTOH Przewalski's horses are just thriving in the Zone!
That sounds quite accurate. The average lifespan of a feral cat in the wild is said to be a year or two. Much shorter than the domestic equivalent.