Imamate (Divinely Appointed Leadership) is a very high position, and it is only Allah who can decide who is qualified for it. And if the Prophet Muhammad (S) announced to the people that the Twelve Imams are the leaders, or that the Ahlul Bayt are the people that we must refer to, or in that Imam Ali is his successor, it was only because he was asked...
Not only the Holy Prophet (S) and his Companions did this act but also past prophets ...
In the Qur'an, there are some verses which ndicate that some people will abide eterna...
His Supplication for himself in Confessing Sins after Finishing the Night Prayer
...But then, he became the object of Divine trials - not for having committed any sin...