Penduko. First of all you cannot cancel your visa. It is only your employer who will apply for its cancellation if you're going home for good. Once your visa is cancelled you have one week to exit Qatar. Otherwise you have to pay a heavy fine for overstaying. NO you can't renew your pataka let alone extend your visa without the consent of your employer. If your visa is cancelled you have to wait for two years before you can work again. If you have NOC that's another story. Two years ban will not apply. I hope this will help in clearing up your confusion.