Earlier this year, my cousin went through some thin ice with his Polaris Indy 600. We needed to wait about 5 days through a deep cold snap for the ice to firm up around it so we could retrieve the snowmobile. With some good old engineering we came up with a winch system and luckily we were able to winch the sled out of the lake where it was resting in about 6 feet of water.
The snowmobile was heavily damaged, the engine has a broken piston in addition to all of the electrical system damage incurred by being underwater.