I personally think if Jesus meant His teachings would end with the life of His Apostles, He would have been recorded by posterity as making that very evident.  But....the Gospel authors wrote their testimony  after the original Apostles had died, the Temple had fallen, and things had radically changed.  Now either the writers of the Gospel were inspired beyond the original Apostles or they were deceiving themselves.  You pick for yourself, for myself, Jesus was referencing future discoveries and that's why these verses are with us today and will always be with us.  The future is to be discovered, not defined by the past.