I lost a retainer in the snow, when I was 16. I found it 6 months later, after the snow melted. I doubt that the microSD card would break though, since it doesn’t have a battery (does it?), so there wouldn’t be any electrical charges going through it. I’d dry it out before using it though, in case there’s some water inside. When the snow starts to melt, go out and try to find it, if you know where you were resetting the phone.