Leave a musical group -- no making a comeback (7)
I believe the answer is:
abandon
'leave' is the definition.
(abandoning is a kind of leaving)
'a musical group no making a comeback' is the wordplay.
'musical group' becomes 'band' (band is a kind of musical group).
'making a comeback' is a reversal indicator.
'no' reversed gives 'on'.
'a'+'band'+'on'='ABANDON'
(Other definitions for abandon that I've seen before include "Forsake, leave behind" , "Lack of inhibition; desert" , "Jettison" , "Leave in the lurch" , "Kick" .)