This is an awful topic! It has only happened a few times in history that dogs were shunned, but even then, they always had a secret following.

In my opinion, no breed in particular would survive long in the wild without a pack. In South and Central America, where packs of feral dogs are the norm, dogs of all sizes belong to the packs. Strength is desired, but intelligence rules the pack. Of course, few or no dogs are "breeds." After a while, when all of the Human characteristics have been selectively bred out, most of these dogs resemble Rhodesian Ridgebacks: Short tan fur or tan with black fur, long thin tails, pointy noses, and ears that flop over at the tips, but not all the way. They are lean, not built wide, with long legs and a straight, slightly arched back. All of these characteristics lend well to a faster runner, not a short distance chest heavy protection dog or a high endurance working dog.

It would also matter where the dog was released. If the only available food is small animals, larger breeds would fare very poorly. Look at relatives like the fox and jackal which are not particulary large, in fact the fox is quite small. These animals thrive where small animals rule. On the other hand, wolves and African wild dogs can be quite large in areas where very large game is prominent. Release a grey wolf in the desert, however, and he would quickly die, but, aside from the climate adjustment, the Jackal would have plenty of food and might even thrive in the north. I can't imagine how quickly a Siberian Husky would die in the desert!

Smaller canine variants are more adaptable because their available food sources are more varied. It is one of the reasons that the coyote's range has grown in the U.S.. It's primary diet is very small animals and anything that it can scavenge. Once again, we are talking about a very lean animal of medium size...