Don't worry about whether they will survive in a pond. As long as there are plenty of aquatic plants in there and some kind of pond filtration, they should do fine. In areas with freezing winters, just make sure there is a breathing hole in the ice after the pond freezes over. If the water is in constant motion via its filtration system, the agitation should keep the surface from completely freezing solid. Goldies tend to go dormant in winter, so they shouldn't be fed after it freezes. Their bodies can no longer properly metabolize the food when in that state, and they really don't need it, then. With the Spring thaw, as temps warm up, they should become active again, and you can resume feeding. Although, in a pond, they can often find their own natural food with insects that land on the surface and the plantlife in the pond. Conservative supplemental feedings probably wouldn't hurt.
I kept goldies in my 65-gallon until they started getting too large, and then I rehomed then in a friend's filtered pond. They are doing fine.
The only other issues could be cats or herons or other predators, and that's just a chance you -- and the goldies -- will have to take. By far, they will be much happier in a large pond, as that is most natural for them. Predation is just how the natural world works. If that's a serious issue for you, the only humane alternative would be an indoor public pond somewhere, or a much larger aquarium, say around 100 or more gallons. Three-hundred would be better, but few people have adequate space in their homes for a tank that large.
So, there are trade-offs.
20 gal. high: planted; 7 white cloud minnows, several RCS, 2 blue shrimp, 5 Amano shrimp, several snails; AC50, Azoo air. 65 gal: planted; 7 rosy barbs, 3 yellow glofish,, 3 zebra danios, 1 rosy red (fathead) minnow, 5 white cloud minnows, 3 dojo loaches, 6 crimson spot rainbow fish, several snails; AC110.