Aren't they made to withstand freezing water? Seems odd if not. I guess I can call the place I got it from to find out for sure. To pull the pump involves dislodging quite a few rocks as it is set in the very bottom of the pond inside a rigid box.
Edited to add: The pond guy advises pulling it IF I think it will freeze down to the pump, although then he said if it is in a vault box it will 'probably' be OK. So, mixed info. I used to have goldfish in this same pond and they always survived the winters, so I assume the water does not freeze solid all the way to the bottom. Or perhaps fish have some coping mechanism for ice.
In any event, it's too friggin' cold at the moment to be digging around in a frozen pile of rocks cemented together with ice so I think I'll just take my chances and perhaps pull the pump during the next thaw. We don't usually freeze solid all winter. Worse case scenario is I buy a new pump next spring. Best case is nothing happens and I just replug the pump when the pond thaws. I'm hoping for Door #2.