Leave a musical group, no returning (7)
I believe the answer is:
abandon
'leave' is the definition.
(to abandon is to leave or desert)
'a musical group no returning' is the wordplay.
'musical group' becomes 'band' (band is a kind of musical group).
'returning' is a reversal indicator.
'no' back-to-front is 'on'.
'a'+'band'+'on'='ABANDON'
(Other definitions for abandon that I've seen before include "Jack in" , "ditch" , "Give up (something) completely" , "dump" , "Leave high and dry" .)