Anti Christ is a misleading person who will be killed by Al-Mahdi (AS). Jesus Christ (AS) will come down from the sky to this earth and will join Imam Al-Mahdi (AS) as one of his supporters and will pray behind him.
The government of Imam Al-Mahdi (AS) will last very long as we read in the narrations that: The rule of the Justice will long as much as the injustice ruled.
The person who claims such claim needs to read more about Imam Al-Mahdi (AS) who is the divine leader who will establish the world government of peace and justice for all human beings.
Wassalam.