Disciple’s end: Earth destroyed! (8)
I believe the answer is:
adherent
'disciple's' is the definition.
(synonyms)
'end earth destroyed' is the wordplay.
'destroyed' indicates anagramming the letters.
'end'+'earth'='endearth'
'endearth' is an anagram of 'ADHERENT'.
(Other definitions for adherent that I've seen before include "Loyal follower, one who sticks" , "Follower, partisan" , "advocate" , "Dedicated supporter" , "One supports" .)