Band member departs with stranger (7)
I believe the answer is:
drummer
'band member' is the definition.
(I've seen this before)
'departs with stranger' is the wordplay.
'departs' becomes 'd' (abbreviation eg in train timetables).
'with' says to put letters next to each other.
'stranger' becomes 'rummer' (rum can mean strange).
'd'+'rummer'='DRUMMER'
(Other definitions for drummer that I've seen before include "One beating" , "One using sticks" , "Gene Krupa, say" , "one of a band" , "dozen Christmas presents" .)