Retreat, due to his almost failing (7)
I believe the answer is:
hideout
'retreat' is the definition.
(I know that retreat can be written as hideout)
'due to his almost failing' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'failing' indicates anagramming the letters (a failed spelling of the word).
'due'+'to'+'his'='duetohis'
'duetohis' with its final letter taken away is 'duetohi'.
'duetohi' with letters rearranged gives 'HIDEOUT'.
(Other definitions for hideout that I've seen before include "Place to lie low" , "sanctuary" , "den" , "retreat" .)