Is he going in to discover it's over? (8)
I believe the answer is:
finished
'over?' is the definition.
(similar in meaning)
'is he going in to discover' is the wordplay.
'going in' is an insertion indicator.
'to discover' becomes 'find' (synonyms).
'is'+'he'='ishe'
'ishe' put into 'find' is 'FINISHED'.
'it's' is the link.
(Other definitions for finished that I've seen before include "Complete" , "wrapped up" , "Done, over, ended" , "Brought to an end" , "dressed" .)