Will the 313 companions of Imam Mahdi (aj) include those who have passed away, or will they only include those who would be alive when the Zuhoor takes place?
Pious waiting believers (Muntadhireen) who passed away before the reappearance of Imam Al-Mahdi (AS) will be raised to be with the companions of the Imam on his reappearance. This is what we read in Du'a Al-'Ahd every morning اللهم إن حال بيني وبينه الموت الذي جعلته على عبادك حتما مقضيا فأخرجني من قبري شاهرا سيفي مقلدا قناتي ملبيا دعوة الداعي في الحاضر والبادي.O Allah; If death takes me from this life, take me out from my grave handling my sword and weapon to respond to his call.
Wassalam.