Partner no longer works, having returned bonus (5)
I believe the answer is:
extra
'bonus' is the definition.
(I've seen this before)
'partner no longer works having returned' is the wordplay.
'partner no longer' becomes 'ex' (ex-partner).
'works' becomes 'art' (I've seen this before).
'having returned' says the letters should be written in reverse.
'art' reversed gives 'tra'.
'ex'+'tra'='EXTRA'
(Other definitions for extra that I've seen before include "One has no lines" , "An additional thing" , "eg Wide; additional" , "One in crowd scene" , "particularly" .)