Imam Mahdi (peace be upon him) does not have an eternal life; rather, he is promised to live a long life. He will appear to people when the circumstances are right to establish justice on Earth. After that, the divine law of death will include him. Almighty Allah said:” Lo! You will die, and lo! They will die;” This long life is not common amongst most people, although it is proven to be for some of them, like prophet Noah (peace be upon him), who lived as a prophet before the flood for 950 years. In some narrations, Khidhr is also alive and he is older than Imam Mahdi (peace be upon him). There is no cause for doubt about the Imam’s existence because of his long life, since the authenticated texts prove his presence and his Imamate.
Repentance is regret and determination to avoid committing sins in the future. Being in the state of purity, prayers or fasting is not part of it. Yes, it is recommended to repeatedly seek forgiveness whenever sins are remembered. A devotee is expected to have high hope in Almighty Allah’s acceptance of the repentance and the forgiveness of sins. Almighty Allah said: “O my slaves who have been prodigal to their own hurt! Despair not of the mercy of Allah, Who forgives all sins. Lo! He is the Forgiving, the Merciful.” (39:53).
The subject of the vow is the correct recitation in the normal way based on the information the person possess. If he paid attention to the mistake during the recitation, then he should correct them. If he paid attention to the mistakes after reciting for some time or after finishing the recitation, then it is not obligated to repeat the recitation correctly although it is better the repeat the verse that was read incorrectly by itself.