Opioid tolerance will absolutely decline if you stop using. it's actually a significant cause of death. People will quit (or go without due to jail, etc) and then relapse with the same dose they has used before and have a fatal overdose.
Morbid but curious question: when tolerance declines, does a de-rated dose (say, 100% of the body's safe mechanical limit) produce the same mental effect as the previous, now way higher dose would? IOW, does the tolerance affect the mental response as well?
(NB. Have integrated the understanding that pushing The Button™ is a generally bad idea. The above is purely intellectual curiosity.)