The Issue that even if only two people would remain on earth one of them would certainly be the Imam, the person with divine authority
5 Aḥadīth
Muhammad ibn Yahya has narrated from Ahmad ibn Muhammad from Muhammad ibn Sinan from ibn al-Tayyar who has said the following. “I heard abu ‘Abdallah 
saying, ‘Would there remain no one on earth except two persons one of them would certainly be the person with Divine authority.”
مُحَمَّدُ بْنُ يَحْيَى عَنْ أَحْمَدَ بْنِ مُحَمَّدٍ عَنْ مُحَمَّدِ بْنِ سِنَانٍ عَنِ ابْنِ الطَّيَّارِ قَالَ سَمِعْتُ أَبَا عَبْدِ الله يَقُولُ لَوْ لَمْ يَبْقَ فِي الارْضِ إِلا اثْنَانِ لَكَانَ أَحَدُهُمَا الْحُجَّةَ.
Ahmad ibn Idris and Muhammad ibn Yahya together have narrated from Ahmad ibn Muhammad from Muhammad ibn ‘Isa from abu ‘Ubayd from Muhammad ibn Sinan from abu Hamza ibn al-Tayyar from abu ‘Abdallah who has said the following. “Would there remain only two people on earth, one of them would the person with divine authority over the other.” Muhammad ibn al-Hassan has narrated from Sahl ibn Ziyad from Muhammad ibn ‘Isa a similar Hadith.
أَحْمَدُ بْنُ إِدْرِيسَ وَمُحَمَّدُ بْنُ يَحْيَى جَمِيعاً عَنْ أَحْمَدَ بْنِ مُحَمَّدٍ عَنْ مُحَمَّدِ بْنِ عِيسَى بْنِ عُبَيْدٍ عَنْ مُحَمَّدِ بْنِ سِنَانٍ عَنْ حَمْزَةَ بْنِ الطَّيَّارِ عَنْ أَبِي عَبْدِ الله قَالَ لَوْ بَقِيَ اثْنَانِ لَكَانَ أَحَدُهُمَا الْحُجَّةَ عَلَى صَاحِبِهِ. مُحَمَّدُ بْنُ الْحَسَنِ عَنْ سَهْلِ بْنِ زِيَادٍ عَنْ مُحَمَّدِ بْنِ عِيسَى مِثْلَهُ.
Muhammad ibn Yahya has narrated from those who he has mentioned from al-Hassan ibn Musa al-Khashshab from Ja’far ibn Muhammad from Kiram from abu ‘Abdallah who has said the following. “If of all the people there will remain only two man one of them will be the Imam. He also said, ‘The last person to die will be the Imam so that no one could complain against Allah leaving him without Imam, the person with Divine authority over him.’”
مُحَمَّدُ بْنُ يَحْيَى عَمَّنْ ذَكَرَهُ عَنِ الْحَسَنِ بْنِ مُوسَى الْخَشَّابِ عَنْ جَعْفَرِ بْنِ مُحَمَّدٍ عَنْ كَرَّامٍ قَالَ قَالَ أَبُو عَبْدِ الله لَوْ كَانَ النَّاسُ رَجُلَيْنِ لَكَانَ أَحَدُهُمَا الامَامَ وَقَالَ إِنَّ آخِرَ مَنْ يَمُوتُ الامَامُ لِئَلا يَحْتَجَّ أَحَدٌ عَلَى الله عَزَّ وَجَلَّ أَنَّهُ تَرَكَهُ بِغَيْرِ حُجَّةٍ لله عَلَيْهِ.
A number of our people has narrated from Ahmad ibn Muhammad al-Barqi from Ali ibn Isma‘il from ibn Sinan from Hamza ibn al-Tayyar who has said the following. “I heard Imam abu ‘Abdallah saying, ‘Would there remain on earth no one except two people one of them will be the person with Divine authority or the second one will be the person with Divine authority (uncertainty is from the narrator).”
عِدَّةٌ مِنْ أَصْحَابِنَا عَنْ أَحْمَدَ بْنِ مُحَمَّدٍ الْبَرْقِيِّ عَنْ عَلِيِّ بْنِ إِسْمَاعِيلَ عَنِ ابْنِ سِنَانٍ عَنْ حَمْزَةَ بْنِ الطَّيَّارِ قَالَ سَمِعْتُ أَبَا عَبْدِ الله يَقُولُ لَوْ لَمْ يَبْقَ فِي الارْضِ إِلا اثْنَانِ لَكَانَ أَحَدُهُمَا الْحُجَّةَ أَوْ الثَّانِي الْحُجَّةَ. الشَّكُّ مِنْ أَحْمَدَ بْنِ مُحَمَّدٍ.
Ahmad ibn Muhammad has narrated from Muhammad ibn al-Hassan from al-Nahdi from his father from Yunus ibn ya‘qub from abu ‘Abdallah who has said the following. “Would there remain no one except two people one of them will certainly be the Imam.”
أَحْمَدُ بْنُ مُحَمَّدٍ عَنْ مُحَمَّدِ بْنِ الْحَسَنِ عَنِ النَّهْدِيِّ عَنْ أَبِيهِ عَنْ يُونُسَ بْنِ يَعْقُوبَ عَنْ أَبِي عَبْدِ الله قَالَ سَمِعْتُهُ يَقُولُ لَوْ لَمْ يَكُنْ فِي الارْضِ إِلا اثْنَانِ لَكَانَ الامَامُ أَحَدَهُمَا.