“A brother is asking whether I believe that our Noble Prophet Muhammad (peace and blessings of Allaah be upon him) was the Seal of the Prophets. Was he the last of the Prophets and the Seal of the Prophets? I say: Yes, but the Qadianis say that the Messiah will return at the end of time so Muhammad is not the last of the Prophets. This is the question; how should we respond?Â
The one who has been given the title of Seal of the Prophets can never have this title taken away from him. If I say that I am going to give a gift to the last of one hundred men, and they come one after another, then the last man comes and takes his gift, now if one of the men comes back again after the last man took his prize, he cannot take it from him.
http://www.islamqa.info/en/ref/91658