Driver who's disappeared in armed conflict (7)
I believe the answer is:
wagoner
'driver' is the definition.
(I know that wagoner is a type of driver)
'disappeared in armed conflict' is the wordplay.
'disappeared' becomes 'gone' (going is a kind of disappearing).
'in' is an insertion indicator.
'armed conflict' becomes 'war' (I've seen this in another clue).
'gone' going into 'war' is 'WAGONER'.
'who's' acts as a link.
(Other definitions for wagoner that I've seen before include "Carter" , "Driver of cart" .)