Re: any chance of thyroid "growing back"?
If the thyroid wasn't completely ablated, that can happen. It is RARE, but possible. IT is the same thing as getting a goiter. When there is thyroid tissue present and thyroid can't function enough to give the body what it needs, more thyroid tissue will grow until it can provide enough or until other problems arise because of it (difficult swallowing, etc).
Theoretically, in your case, a tiny amount of thyroid tissue might have remained alive. If you have been undermedicated for a long period of time, which is all too common, your tiny little thyroid may be trying to grow back to give your body what it needs.
Again, this is rare, but it might be worth checking in to. What has your TSH been maintained at since your thyroid was ablated? If it has been kept above 2 for long periods of time, I would think that would increase the chances of that happening.