A lot of the soldiers who got hooked on heroin in Vietnam quit using when they got back to the States. The heroin which was available at the time in America was utter crap next to the H they were getting in the Nam: there was also a change of place and situation which made it easier for them to leave their habit behind once they got stateside.
My father became physically addicted to morphine after getting wounded in Korea. Once he kicked it, he felt no further desire to use again. I also know a friend who became physically addicted to oxycodone after an operation. She was dopesick for a few days (and mightily pissed off at her doctors), but never went back to using. I've gathered this is also the case for many people who become addicted to prescribed drugs. Once their condition is cured and they get through withdrawal, they have no desire to continue taking the drug.
The whole myth of the inherently seductive and addictive properties of opiates comes from the 19th and early 20th century, when there was a huge push to regulate their distribution and prescription. About that time the myth of "soldiers' disease" (widespread addiction to morphine and opium among Civil War soldiers) begins. The idea was to make opiates look like a deadly poison which could ensnare even the most dewy-eyed innocent if they were used regularly. This meant they could regulate doctors because, after all, they were just Protecting the Children from the evils of abused prescription drugs. (Sound familiar?)
There's some truth to "once a junkie, always a junkie." If you were once psychologically addicted to a substance, chances are good that your addiction will return if you start using again. But there's a huge difference between physical and psychological addiction. You can have one without the other -- and for the purposes of long-term sobriety, it is the psychological addiction which matters.
(I'm currently writing a book on P. somniferum and its various derivatives, so I've been studying the subject at some length. And let me just say that I have truly enjoyed the hell out of my research

).