Your husband was quite fortunate to receive a Section 212(c) waiver. As you know, the Section 212(c) waiver is rare as the law was modified in 1996 so a very limited set of individuals still qualify for the waiver.
With that said, because your husband received the Section 212(c) waiver, he still has the opportunity for naturalization. However, there will be additional factors involved, and the matter can be quite complex.
You should contact an immigration attorney to assist you with the matter, and I would suggest you contact my colleague, Ms. Yenniffer Delgado, at 404-387-0756.
DISCLAIMER: Although I am an attorney, absent a signed retention and engagement letter, I am not your attorney. There are no exceptions to this rule. Moreover, you shall not rely on the information I am providing you, as it is only for your general knowledge and educational purposes. Indeed, my analysis is always based on the laws of Georgia, and your jurisdiction might have substantially different laws and requirements. As such, you should always contact an attorney that practices in your local area.