Is he going in to discover it's all over? (8)
I believe the answer is:
finished
'all over?' is the definition.
('finished' can be similar in meaning to 'all over')
'is he going in to discover' is the wordplay.
'going in' is an insertion indicator.
'to discover' becomes 'find' (finding is a kind of discovering**).
'is'+'he'='ishe'
'ishe' inserted into 'find' is 'FINISHED'.
'it's' acts as a link.
(Other definitions for finished that I've seen before include "Ended. completed" , "dressed" , "wrapped up" , "exhausted" , "Done, over, ended" .)