If nothing else, finally grasping theme without them (2,5)
I believe the answer is:
at least
'if nothing else' is the definition.
(I've seen this before)
'finally grasping theme without them' is the wordplay.
'finally' becomes 'atlast' (synonyms).
'grasping' is an insertion indicator (inserted letters are held or grasped).
'without' is a deletion indicator.
'theme' with 'them' taken out is 'e'.
'atlast' going around 'e' is 'AT LEAST'.
(Other definitions for at least that I've seen before include "however" , "As a minimum" , "'If nothing else (2,5)'" , "Eat salt (anag) - if nothing else" , "Anyway" .)