Will a person be rewarded for quitting "Nasheeq" after using it for five years? Will his suffering in doing so be counted among his good deeds? And will Allah forgive him for the past years during which he consumed this substance?

The use of snuff is religiously prohibited. A Muslim is rewarded for abandoning prohibitions seeking Allah's pleasure. For whoever abandons a sin for the sake of Allah, a good deed is recorded for him. If he abandons it out of forgetfulness, then there is neither reward nor sin upon him. But if he abandons it due to incapacity after striving for it, he is like one who committed it. The fatigue and suffering incurred from abandoning prohibitions for the sake of Allah are rewarded, as Allah Almighty said: {That is because they are not afflicted by thirst or hardship or hunger in the cause of Allah… except that it is recorded for them as a righteous deed}. For Allah recompenses for voluntary actions and what results from them. And Allah is too generous to reject a sincere penitent, and He loves those who repent, and He forgives all sins; rather, He replaces the evil deeds of the penitent with good deeds, and one who repents from a sin is like one who has no sin.