Not having left of one’s own accord, as it proved (6,3)
I believe the answer is:
turned out
'proved' is the definition.
('turn out' can be a synonym of 'prove')
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for turned out that I've seen before include "Attired" , "Dismissed" , "Ended up" , "Produced - proved - dressed" , "emptied" .)