Question: Does saying, “Isa will come back to earth in the time period close to Doomsday,” not come to mean, “Our Prophet could not carry out his task. Isa will complete it”?
ANSWER
Such a claim is very abominable. Each prophet fulfilled his task. When Musa ‘alaihis-salam was spreading his religion, he wanted Harun ‘alaihis-salam, his brother, to assist him. Thereupon, Allahu ta’ala sent his brother Harun ‘alaihis-salam as a prophet to help him.

Just as the Blessed Companions served in order to spread our religion, so all of the Islamic scholars who will come until the end of the world will keep serving it. This service is a command of our religion. It never means that our master the Prophet could not perform his task. In fact, it is the first duty of each Muslim to work for it as much as he or she can. Hadrat Mahdi and Companions of the Cave, too, will join this service. ‘Isa ‘alaihis-salam requested Allahu ta’ala to make him a follower of our master the Prophet, and his request was granted. In the time period close to Doomsday, he will come as a member of this Ummah, not with the task of prophethood. He will strive to promulgate Islam and will eradicate all other false religions, including Christianity. As a matter of fact, a Qur’anic verse purports:
(It [Hadrat ‘Isa’s descending from the sky in the time period close to Doomsday] is surely knowledge which shows the approach of Doomsday. Have no doubt about it. Follow me; this alone is the true path.) [Surat-uz-Zukhruf 61, Baydawi]

Our master Rasulullah explains this verse by saying:

(I swear by Allah that ‘Isa will descend from the sky as a just judge. He will break the cross [he will wipe out Christianity], kill pigs [he will forbid pork], and prohibit everything other than Islam.) [Bukhari, Muslim, Abu Dawud, Tirmidhi, Ibn Abi Shayba]

(When ‘Isa returns to the earth, he will marry, have a son, live for about 40 years, and die. He will be buried beside me.) [Tirmidhi, Mawahib]

‘Isa ‘alaihis-salam said, “The emergence of Dajjal is a sign of Doomsday. I will descend from the sky and kill him” (Muslim, Ibn Maja, Abu Dawud, Imam-i Ahmad, Tabarani, Imam-i Suyuti, Imam-i Munawi, Imam-i Nawawi, Kanzil ummal, Majml zawaid).

No Muslim can reject any of the hadith-i sharifs above.

Islamic scholars are like prophets
Question: Since no prophet will succeed our master the Prophet, is Hadrat ‘Isa’s return as a prophet not incompatible with the Qur’an? In the past, a rasul with a new religion used to be sent every thousand years. Now no prophet is sent after our Prophet, even though a thousand years have passed. What may be the reason for it?
ANSWER
Hadrat ‘Isa will not come as a new prophet, but will come in order to strengthen Islam. Hadrat Mahdi, too, will come with the same mission. In the past, anbiya [pl. of nabi] used to be sent, and they used to strengthen the religions brought by rusul [pl. of rasul]. After Muhammad ‘alaihis-salam, this mission has been performed by Islamic scholars succeeding him. Therefore, our master the Prophet stated, “The scholars of my Ummah are like prophets of Israelites” (Imam-i Yafii, Imam-i Rabbani, Abdulghani Nablusi, Nashr-ul-mahasin).

Hadrat Imam-i Rabbani stated:
When ‘Isa ‘alaihis-salam descends from the sky and follows the religion of the Prophet of the latest time, his [Hadrat ‘Isa’s] reality will rise from his own rank, and since he will follow him, it will ascend to the rank of the Muhammadan reality (haqiqat-i Muhammadi). It will strengthen his religion. For this reason, in the earlier dispensations, after an arch-prophet a new prophet used to be sent within a thousand years. With those prophets, the religion of that arch-prophet used to be strengthened. When the period of time appointed for his religion came to an end, a new religion with an arch-messenger used to be sent. Since Muhammad ‘alaihis-salam is the last of the prophets and his religion will never be able to be changed, the scholars of His Ummah are like prophets. The task to strengthen Islam has been entrusted to them. Though the number of scholars is few who will come a thousand years after the demise of the Messenger of Allah, they will be in the highest degree so that they can strengthen Islam thoroughly. Apart from them, an arch-prophet [Hadrat ‘Isa] will also be assigned to strengthen his religion. (Vol. 1, Letter 209)