Obliteration is certain after time (7)
I believe the answer is:
erasure
'obliteration' is the definition.
(I've seen this in another clue)
'certain after time' is the wordplay.
'certain' becomes 'sure' (synonyms).
'after' is a charade indicator (letters next to each other).
'time' becomes 'era' (era is a kind of time).
'sure' put after 'era' is 'ERASURE'.
'is' is the link.
(Other definitions for erasure that I've seen before include "Rubbing out - English synthpop duo" , "Wiping out - English pop duo" , "Obliteration - rare use (anag)" , "Censorship" , "clearing of tape" .)