They are probably hibernating (or the equivalent of such) at this point. If you choose to do this, I would allow the water in the container they are in to slowly warm up over the period of a few days.
I live in the US with similar weather. There are weather loaches that have taken residence in local, stagnant ponds near where I work. They are actually an invasive species in North America, Eastern Europe, and Australia due to their adaptability.
I would leave them out there.