Going back for key-holding worker, left alone (8)
I believe the answer is:
orphaned
'left alone' is the definition.
'going back for key-holding worker' is the wordplay.
'going back' says the letters should be written in reverse.
'for' becomes 'pro' (I've seen this before).
'key' becomes 'e' (I've seen this in other clues**).
'holding' indicates putting letters inside.
'worker' becomes 'hand' (hand is a kind of worker).
'pro' written backwards gives 'orp'.
'e' put inside 'hand' is 'haned'.
'orp'+'haned'='ORPHANED'
(Other definitions for orphaned that I've seen before include "Having both parents dead" , "Left without father or mother" .)