One of the points in the traditions mentioned above is that each of the twelve will be from the Quraysh. After them there will be chaos. Another point is that the religion will remain established till the twelve Caliphs of Quraysh are present. When they die, the earth will swallow its inhabitants.
The above two points thus prove that after the twelve Caliphs of the Holy Prophet (s.a.w.s.) the earth will be destroyed.
Therefore it is necessary that one of these twelve successors should have such a long life that it should surpass the age of this earth.
This is exactly how it happened. The Twelfth successor of the Holy Prophet (s.a.w.s.) was bestowed with a long life. He is Al-Mahdi Muhammad ibn Hasan Al Askari (a.s.).
The traditions discussed in this treatise prove the Imamat of these Twelve Noble Personalities. Not anyone else.