Life Expectancy

Is our Mutah contract with a duration of 99 years invalid if it surpasses our lifespan? We intend to terminate it before that occurs, is it still considered invalid? Zaid Alsalami	If there was no threat to the life of Imam al-Mahdi, and so there was no occultation, would he have lived a normal lifespan? If so, would there have been more than 12 Imams or would the world have ended early? Sayyed Mohammad Al-Musawi
Is it possible that Allah increase or decrease someone's lifespan due to someone else's prayer for or against them? Sayyed Mohammad Al-Musawi	Is there a du'a one can recite to increase one's lifespan? Nasim Walji Pirmohamed