Yes, koi will survive in a pond over the winter.
What is important is that the pond be deep enough
to not to freeze solid over the winter.
Someone will hopefully post and let you know what
works in upper Wisconsin.
In the winter it is important to keep a hole open in the ice
for exchange of gases.
I use a protected air pump, line and air stone. Zone 7
here in SE WA, I'm sure you're much lower on the scale.

kathy