it depends where in the world they are really and the strictness of the family around them. for instance, in iran, converting from islam to judaism is punishable by death.
apparently every year 6m muslims convert to christianity. not sure how true or accurate that is. i did find this though:
"There's a certain hadith [verse] that said if anyone changes his or her religion, he deserves to be killed. In my research, I found that was linked to some people who were trying to penetrate the Muslim community at the time in Medina. They came from Jewish or pagan communities, and announced they had become Muslims. Then after a few days, they announced they had found this religion to be very bad and they had decided to go back to their religions: Judaism, paganism, whatever.
"The Prophet was trying to stop that kind of conspiracy so he said that if anyone changes from the religion he has adopted, we will kill him. Islamic jurists [ scholars] have not paid attention to [the exceptional nature] of that event. They have generalized that hadith to say if anyone practices apostasy, we should kill him."
of course it only takes one numpty cleric somewhere to interpret it a certain way, and all hell breaks loose.