I have lost one out of 12 so far - and that was due to a dead queen at the height of Winter... found her on the bottom board of an empty hive. These bees were generic Italians. My remaining feral/survivor bees are booming right now. Even the one that I overwintered with four frames of bees and honey. I have one more hive of generic Italians that seem to be barely hanging on too. Planning on giving them a new queen soon.
One of my friends overwintered a three frame nuc with one of my wild queens and they are plugging right along too. I am thinking I should make it a priority to breed from my wild bees this year.
My feral/survivors are all from 3rd year or older wild hives and queens. I do feed them at times, but really do nothing else for them except for using juniper/creosote bush smoke in my smoker. I noticed most of my bees still have the fall feed I gave them in October stashed away - I colored it blue with food coloring (I know - not very environmentally friendly I suppose).