As you have rightly mentioned in your message to us, there is hadith narrated by Abu Basir from Imam Sadiq (a.s) in which the disintegration of a dynasty following the death of an individual called "Abdullah" has been prophesied and there is also a glad-tiding in the narration as per which there is not so much time gap between the disintegration of that government and the reappearance of Hazrat Mahdi (a.s.).
Considering the object of your question, two points should be taken into account:
1- It is not known for sure whether Abdullah in the question refers to the same existing individual who is now being considered by some individuals and media as the manifestation of this narration.
2. The narration which you have mentioned in your message does not exist in trustworthy Shiite or Sunni sources. As a general principle, if some comes to you with a hadith, you should try to verify the chain of its transmission (sanad) and if the Arabic text of the hadith is available, you can easily trace it in reliable hadith books by using special hadith software. May Allah grant you success.
 - Shaykh Tusi, Muhammad bin al-Hassan, Al-Ghaybah, pg.447, Maaref Islami Institute, Qom, 1411 A.H.