According to a Hadith: Imam Mehdi (as) would definitely appear in this world, even if the last day of Qayamah occurred, and Allah would prolong that day.

It simply means that even God isn't aware of the exact time of Imam Mehdi (as)'s arrival. It is with great regret to say that the Muslims know nothing about Imam Mehdi. And what Tahir Ul Qadri has said is a great conspiracy against His Sublime Eminence Imam Mehdi RaRiaz Gohar Shahi. Tahir Ul Qadri in the same speech said, "Words of the Qur'an would disappear from the books of Qur'an, and the pages would be left blank". Tahir ul Qadri perceives the lifting of words from the books to be the lifting of the Qur'an.

First of all, the Qur'an was not in form of a book at the time of the Hadith and the Qur'an wasn't revealed unto a piece of page. The Qur'an was revealed on Prophet Mohammad (saw)'s heart. If the Qur'an is to be lifted, it would be lifted from the heart of the Prophet. What is the lifting of the Qur'an? It is the non-availability of men who have obtained Spiritual Grace of the Qur'an from the heart of Prophet Mohammad (saw). The Qur'an was revealed unto the heart of the Prophet Mohammad (saw). Yet Gabriel was accompanied with the Qur'an (Wahee). The Qur'an that which the Muslims regard as the most authentic of all celestial books, and which Allah has promised to guard against all evil interference has become subject to an academic and explanatory crisis. Translations of the Qur'an have played a havoc, and explanations by ignorant clerics have given birth to more than 73 different sectarian elements within Islam. What authenticity do you think lies in the collection of a'hadith? A'hadith are words of the Prophet (saw).

When Allah's word has been made subject to a great deal of academic fiddling and modification in the explanation and transliteration, what authenticity could there be left in the collection of a'hadith, when it hasn't even been collected, compiled, published with the presence of Gabriel? Reliance on a'hadith in a matter as delicate as that of recognition of the Awaited Imam Mehdi (as) is a great folly. 
This is because a'hadith are not as authentic as they were at some time in remote history. Why does Tahir Ul Qadri not comment on the appearance of His Sublime Eminence Sayedna Gohar Shahi's images on the Moon, the Sun, Mars, the Holy Black Stone? This but an extreme form of arrogance to ignore completely the signs that Allah has manifested to announce the identity of the Awaited One.