I don't think science has the answers to some of your questions yet. But people here at Freedom and people you know in your real world settings can shed some great insights for you. First, I suspect most things do return to normal. I just brought up the post I feel 100% Better Since I Quit!
If dopamine actions were permanently messed up in ex-smokers, I don't think you would hear many people express this sentiment. Sure they might breath better, but most people who express this statement are talking more than just breathing.
Most people find out that within a few weeks of quitting smoking, they are calmer than they ever were when actually smoking--or at least back to their baseline. Most claim they have more energy, and many people who I have had in clinics who were found that there overall concentration improved. When these people are students, they often subsequently find their grades and study patterns improving too.
Some of them attribute this effect to being able to concentrate at the tail end of classes more so than they could while smoking--basically being in withdrawal and focused on getting out of class as fast as they could as opposed to be focusing on the subject matter. Again, if dopamine were permanently messed up I don't think you would see these kind of performance enhancements.
In the first few days of quitting things are a bit out of whack for people. But shortly things do fall in place. One other thing I should point out--dopamine does not answer the whole story when it comes to nicotine addiction. Keep in mind, most other drugs also elevate dopamine. But the addiction to nicotine is very specifically an addiction to nicotine. By that I mean they only way a person is going to relapse to nicotine is by readministering nicotine.
Taking another drug that elevates dopamine does not cause nicotine withdrawals or a nicotine relapse. Accomplishing a great feat and releasing dopamine naturally does not cause the person to go through a full three days of nicotine withdrawal. It may trigger the thought for a cigarette--but that is likely much more from the association that they used to smoke when they felt this level of excitement. Or, as in the case of the new findings here, if they hold up to further testing, they may have smoked to celebrate not so much to just pour in more dopamine, but rather to inactivate acetylcholine making the thrill of the accomplishment last longer.
Again, listen to ex-smokers and listen to your own bodies. You will likely hear the obvious--that you feel better, are healthier and will probably live longer and have a better quality of overall life as long as you always remember to never take another puff!