The body responsible for this is the Shura Council - a kind of "council of the wise" of the organization. The secretary general is elected for a period of three years. When Nasrallah was first elected Secretary General 32 years ago, it was reported that Iran had complete influence over the members of the Shura Council. There is no reason to assume that the situation is any different today.

It is not yet clear when the Shura Council will convene. According to reports, Naim Kasem who is officially the deputy secretary general will serve as temporary secretary general. Kasem is considered a gray figure and his last appearance in public was last Sunday at the funeral of the senior military officer Abraham Akil.

Nasrallah's cousin Hashem Safi al-Din will probably be the one chosen as the next secretary general by the Shura Council. According to Saudi sources already in 2008 it was decided that he would replace Nasrallah when the time came. 

All this is true to the extent that he actually survived the attack in Dahiyeh.