All perfect praise be to Allah, The Lord of The Worlds, and may His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
Getting killed is what Allah, The Almighty, Has Protected His Prophet (PBUH) from; therefore, he (PBUH) dismissed his guards after the above verse was revealed. However, the disbelievers managed only to harm him in the Battle of Uhud and other battles.
Allah, to whom be ascribed all Perfection and Majesty, has also protected Prophet Mohammad (PBUH) against making any mistake in delivering His message to mankind for He says, "Nor does he say (aught) of (his own) Desire." {An-Najim/3}. He, The Almighty, added, "He who obeys the Apostle, obeys God" {An-Nisa`/80}. This is in addition to many other verses and narrations indicating that obeying the Prophet (PBUH) is incumbent upon every Muslim. Besides, if there been any defect in his delivery of the divine message, Allah wouldn`t have enjoined obeying him.
Although Prophet Mohammad (PBUH) was bewitched, Allah Healed him and that magic hasn`t affected the rules of Sharia which he was entrusted to deliver.
Moreover, Allah Has Said about those who raise suspicions in this regard (What means): "Fain would they extinguish God’s light with their mouths, but God will not allow but that His light should be perfected, even though the Unbelievers may detest (it). It is He Who hath sent His Apostle with guidance and the Religion of Truth, to proclaim it over all religion, even though the Pagans may detest (it)" {At-Tawbah/32-33}. Skeptics had better have a closer look at the situation of other religions in order to arrive at the conclusion that Allah, The Almighty, Has Protected Islam and Muslims against every harm. And Allah Knows Best.
