My thoughts on this would be it they have frozen and remained frozen they would be like it you had froze them in your freezer. But if they have thawed out, warmed up and froze again wouldn't be something I would want to use. If they have really frozen and then warmed up for a while I would say they would be soft and mushy. I have a refrigerated chest type drink box I have used to store our onions in. The temperature control on those boxes seem to vary and have a wide differential. I know I have seen 32 F on the thermometer in the box and maybe lower but the temperature doesn't get above say 45 F at the most. I know the term froze for you can be a lot colder temp than what we would normally see. We did have a low of like 26 F last night which is cold for us. Hoping my broccoli and cabbage I still have growing survives. I just harvested some broccoli and a couple small heads of cabbage this week. Fresh homegrown broccoli and cabbage for Christmas dinner. My wife made broccoli and cabbage slaw. It also had carrots from the garden that had just been harvested. I didn't plant my onions last spring so the onions were store bought.