Old writer expired not achieving closure (4-5)
I believe the answer is:
open-ended
'not achieving closure' is the definition.
'old writer expired' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'writer' becomes 'pen' (I've seen this before).
'expired' becomes 'ended'.
'o'+'pen'+'ended'='OPEN-ENDED'
(Other definitions for open-ended that I've seen before include "With no fixed limit, not circumscribed" , "Allowing free debate with no set time to finish." , "Without fixed limits or restrictions" , "Having no fixed limit, perhaps a discussion" , "Having no predetermined limit" .)