Yan, you could consider putting a simple "low tunnel" made of PVC pipes and clear plastic sheeting over your garlic for a little extra protection. Last year I planted onion sets in the fall that grew to about a foot tall before winter set in; I covered them with a low tunnel and they never missed a beat, just paused and then continued growing again when the weather warmed up. But I actually think that the worst that will happen to your garlic in any case is that the tops will die back and it will start growing again in the spring, which will likely weaken the plants a bit and your bulbs will be a little smaller than they might have been otherwise. I'll actually be very interested to hear what does end up happening, if the tops don't die back then the bulbs will likely be larger than they would normally be.
