Leave a musical group, never to return? (7)
I believe the answer is:
abandon
'leave' is the definition.
(to abandon is to leave or desert)
'a musical group never to return?' is the wordplay.
'musical group' becomes 'band' (band is a kind of musical group).
'never' becomes 'no' (I've seen this in other clues).
'to return?' shows that the letters should be reversed in order (I've seen 'returning' mean this).
'no' written backwards gives 'on'.
'a'+'band'+'on'='ABANDON'
(Other definitions for abandon that I've seen before include "Give up (something) completely" , "Wantonness: desert" , "Forsake, leave behind" , "Lack of inhibition; desert" , "Stop" .)