Is he who says that the Awliya (saints) have a خاتم (seal) a disbeliever, and what is the proof for that, and does this entail not smelling the fragrance of Paradise?

The term "Seal of the Awliya'" (Seal of the Saints) is an invalid appellation that has no basis in the Qur’an, the Sunnah (definition), or the sayings of the Salaf. However, the last pious believer is the last of Allah's Awliya'. Allah Almighty's Awliya' do not have a specific "seal" as the prophets do.

As for declaring someone who asserts the "sealing of sainthood" in a specific person to be a disbeliever, there is no evidence for their disbelief, and the fundamental principle concerning a Muslim is that they are free from disbelief.