Back in or back on? It may just sit there on top of the ice.
Boats are probably better off in the water in these temps as the water is usually a bit warmer than the air and less likely to get frost damage.
We were mean't to be going to the boat this weekend but I think I'll give it a miss, 2 weeks ago when I left it I was hovering on the idea of not winterising as "we're over the worst now", very glad I did but still a bit worried about the calorifier and water tank, engines should be fine.