Left share covered by legal agreement (8)
I believe the answer is:
departed
'left' is the definition.
(departing is a kind of leaving)
'share covered by legal agreement' is the wordplay.
'share' becomes 'part' (synonyms).
'covered by' is an insertion indicator.
'legal agreement' becomes 'deed'.
'part' going inside 'deed' is 'DEPARTED'.
(Other definitions for departed that I've seen before include "Left, went away" , "Dead; set off" , "completely breathless" , "Went - dead" , "Gone, maybe dead" .)