Paul, if the ground freezes you will lose them, if they are showing new growth and we have a late frost, that will knock them back by weeks. What you need to do is keep enough large buckets or pots to hand so if a frost is forcast, you can put a pot over them for the night. Another thing is that they will grow very bushy, this is another reason to start them off in shallow compost, when the sprouting tips or shoots are about half an inch long the tubers should be cut into several pieces with a strong sharp knife. If two shoots are coming from one tuber you can cut it in two keeping a piece of tuber with each shoot. Could you buy another one and try that out for yourself??? I have in the past turned my twelve plants into forty eight plants and given thirty six away. I was not in the greatest of health last autumn and I left mine in the ground and lost them all, some were thirty years old. More correctly they were what I had been cutting up and growing for thirty odd years. If you want to leave them in the ground, let a frost hit them and that day cut them off about six inches above soil level. Cover with a couple of layers of plasic or polythene and a bucket with a brick on top to prevent it from blowing away.
Good luck.