It's not advisable to stop any prescription pain pill "cold turkey" bt most posters on OCF did not have any major issues in reducing their dosage as the pain subsides. The key is to take it slow.
I've been on both sides of opiate use : done for recreation when truly normal and for pain relief for the new normal. I don't think you husband is "addicted" in any way, he just needs a schedule to reduce dosage. Doctors should be more explicit in my opinion in helping quit taking pain pills with instructions on splitting pills when possible as a wind down after getting smaller dosages.
Mouth ulcers were indeed terrible and seltzer water helped me even though it burned.
Charm