AQ will do the damage it can do with Z alive or with Z dead. The difference is that with Z dead they do not have the focus, drive, and ability of a master to direct their activities and their actions will be less efficient. Z's death has no upside for them, regardless of the breastbeating frenzies of the Islamist Press (NYT, WaPo, etc.)
And where are you sleeping tonight Zawahiri, in a nice hotel? In your family home? Or, in some tight place straining to hear if that small noise in the night might be a drone or some far away bomb release. Do you examine your associates closely to determine the Judas in your midsts.
You know the angel of death approaches, but you know not the time of it's arrival.