Do you only need to bring your pond fish in for the winter if there's a chance that the water will freez over?

oh, and can you keep koi and tank goldies together?

It depends on the tank goldies. Faster fish like comets and shubunkins do fine with koi, and are doing great in the pond, even in cooler temperature. Other goldies are a bit different.
Koi can stay in the pond if you have a little heater in there that keeps a small portion of the pond surface free of ice, so the oxygen exchange can take place. Koi pretty much *hibernate*, that means, they stay in the deepest part of the pond when it gets cold, and hardly move. Their metabolism stays low, they dont eat, and their breathing gets also slower. Where do you life, and how cold exactly is *cold*?
I have ranchu, orandas, my Bristol shubunkins and a big comet out in the pond even during the winter, although I wouldnt consider a Central Florida winter anything close to a winter up north. The lowest temps they had to endure last year was in the 30s a day or so, but they were covered up in sheets of foam, and the airpumps shut off, no food. I wouldnt leave them out in that cold water for longer periods though....
Hope that helps a bit....

I kept all my fish in my pond two winters ago and they were fine. Last year all of them died even with a heater. It just got too cold and we got too much snow. I have Koi, Shubunkins, Comets, Fantails and Oranda's. So this year all of my fish are living in the basement. My dad set up rubbermaid feeding troughs and grow lights for me. They are doing wonderful and I bet are happy to not be out freezing (the pond had ice on it this morning).