Did Muhammad leave Mecca because he lost Abu Talib’s protection?
Prophet Muhammad’s reason for emigration was not because he, “lost his most influential protectors.” Prophet Muhammad left under Divine guidance, as God informed him that the Meccans were plotting to assassinate him once again. After suffering the most brutal persecution ever witnessed in history for roughly twelve years, Prophet Muhammad and the Muslims did not raise a single sword or pick a single fight. Rather, they left under cover of darkness and fled for their lives, as Sufi Mutiur Rahman Bengalee writes:
When the Meccans came to know that the cause of the Prophet was making rapid and steady progress, they now resorted to a new plan to put an end to the Prophet’s life and cause. They selected one man from each tribe who pledged himself to assist in making a united assault in order to assassinate the Prophet at night when he was asleep so that the guilt of the crime would be evenly distributed. If they could kill the Prophet, they believed it would be impossible for the Prophet’s people to stand against the combined tribes of Mecca. 
Muhammad, however, received a revelation, which warned him of the danger; he was commanded by God to leave town and seek refuge in Medina. A substitution had to be made, so his cousin Ali volunteered to lie down upon the prophet’s bed. With tears in his eyes he gazed at the Ka‘’aba and said: ‘Oh, Mecca, thou hast been to me the dearest spot in all the world, but thy sons would not let me live here.’  The Prophet’s enemies found Ali in Muhammad’s bed. They were so angry that they put Ali in confinement, but finding such procedure useless, they soon released him. A bounty of 100 camels was placed on Muhammad’s head, dead or alive. 
Thus, the decision to leave, was a painful event in Prophet Muhammad’s life, when he was forced to leave his homeland to escape assassination. Prophet Muhammad left to flee persecution—precisely as the Christian scholar Waraqa ibn Nawfal foretold twelve years prior.
Critics also ignore that Prophet Muhammad’s decision to preach or not, and his decision to migrate or not was not based on whether he had Abu Talib’s protection. It was in fact Abu Talib who insisted he wanted to protect his nephew and thus that protection remained. Prophet Muhammad, however, made clear that his protection was not from any man, but from God alone—as per God’s promise to him in the Qur’an: “O Messenger! Convey to the people what has been revealed to thee from thy Lord; and if thou do it not, thou hast not conveyed His Message at all. And Allah will protect thee from men. Surely, Allah guides not the disbelieving people.”  Prophet Muhammad did not migrate due to a lack of protection from other men. His migration, in fact, was based upon Divine guidance to escape assassination.
 Sufi Mutiur Rahman Bengalee, The Life of Muhammad 67 (Kessinger Publishing 2010).
 Id. at 67.
 Id. at 68-70.
 Qur’an 5:68.