Even in Queensland in winter our water gets cold enough to kill guppies during winter. Usually I have noticed the males die off first then if the cold persists the females start subcoming to the cold. However usually enough females and juvi males will survive winter to restock a pond in spring once the water begins to warm again. I am not condoning the wanton possible cruelty of leaving a fish well outside of its comfort zone and natural habitat variation, but I have in the past tried to keep guppies year round in a pond without adding heaters.
Another factor I found that encouraged the survival of guppies through winter in an unheated pond was plenty of organic matter on the floor of the pond that as it decomposed released warmth in to the water.
As for cherry shrimp surviving winters outdoors, I have heard of them surviving under ice outdoors, they really are the hardiest of shrimp. But I dare say that pushing the shrimp to their extremes could have weakened them to suffering secondary infections later down the track, it also would have severely curtailed any breeding and shell shedding the shrimp would have done in more acceptable temperatures.
