A single major sin does not erase all good deeds, but it may erase an equivalent amount of them, according to the opinion of most of Ahl As-Sunnah. Nothing erases all good deeds except disbelief, just as nothing erases all bad deeds except a sincere repentance.

Determining whether someone is a kafir or a fasiq is not up to us, rather it is up to Allah and His Messenger (peace and blessings be upon him). No one may be judged to be a kafir or fasiq except the one whom the Quran and Sunnah indicate is a kafir or fasiq.