This implies that Allah never left the human on the earth...

This implies that Allah never left the human on the earth without His representative. At the time of the prophets, the Hujjah were the prophets. Now that there will be no prophet after , the Hujjah is his living Ahlul-Bayt at each era till the day of resurrection. The necessity of the existence of a Hujjah on the earth follows that this world will end when the last Imam passes away. Beside what we quoted from Quran, let us quote some traditions from Sunni sources to support the above assertions.