Apostate prophet diggs in old polemics; he might bring up ibn abi Sarh?

In answer to the video "Allah is Merciless"

Another typical example is that of Abdullah Ibn Sad Ibn Abi Sarh who had converted then apostised, joined the enemy side and began undermining the authenticity of the Quran by spreading rumors that he had been forging verses. He in addition incited the opposite party to war. When the Muslim side finally overcame against all odds and his own inciting efforts, his inevitable, legitimate fate was now execution for high treason.

This is what governments generally do once a traitor is apprehended, especially when a conflict ends while the person is still among enemy ranks. At that point, ibn Abi Sarh sought Uthman's intercession and came to the prophet to pledge his allegiance. The prophet ignored Uthman's plea twice before finally accepting. The prophet knew that he deserved to be put to death but at the same time, because of the general amnesty he had declared upon Mecca's conquest, he hesitated in the case of Sarh' special case, leaning more towards the capital penalty. By his silence, he left it to the attendance of close followers to do as they liked and as he saw that they leaned the opposite way, he reluctantly validated their judgement and accepted Sarh's pledge. 

However and as already shown from the Quran, should one leave Islam peacefully without intending any harm to the community, not combining apostasy with public rejection of the state system, which includes refusal to acquit oneself from fiscal obligations, then the consequences of the sin are left for the Creator to decide in the Hereafter. A case in point is that of a bedouin that apostised though he had accepted Islam, pledging allegiance in front of the prophet the day before. The prophet did not punish him, the most that he did was to ignore him 3 times before stating

"Medina is like a furnace. It expels its impurities and collects what is pure".

The early caliphs followed the same line. Umar Ibn Abdul Aziz did not bother a group of apostates so long as they did not rebel against government laws.  It is thus rejection of the religion in a way that threatens the stability of the Islamic system in place that warrants death penalty. These were the cases covered by the prophet's saying

"Whosoever changed his Islamic religion, then kill him".

In fact there are explicit reports where the prophet let people leave the community in security following their spiritual apostasy.

Once more, there is no compulsion in religion 2:256,18:29 so no punitive measure can be directed at an apostate neither can he be compelled to go back to Islam or forced to repent solely on the basis of his choice of creed. Per the Quran and as made clear in 4:88-90 quoted earlier, action is to be undertaken against an apostate when he engages in hostile behavior towards Muslims and the Muslim state. Fighting, punishing or killing an apostate has therefore nothing to do with a person's choice of creed but with his behavior towards the Muslims.