The alligator gars have been through one winter outside, and the longnose gars have been through two winters outside. The pond does freeze over, but there are usually a few small holes to allow for air exchange; it also doesn't typically stay frozen for longer than a few weeks to a couple of months.
Based on a few quick glimpses I've caught of them plus damage I've found on some large dead bass & catfish, the alligator gars are very much alive & well. Not too sure on the longnose gars, but I would imagine that they're doing fine, too.
