Nothing more than a 50-50 chance, nevertheless (4,2)
I believe the answer is:
even so
'nevertheless' is the definition.
('even so' can be a synonym of 'nevertheless')
'nothing more than a 50-50 chance' is the wordplay.
'nothing' becomes 'o' (looks like zero - 0).
'more than' is a charade indicator (letters next to each other).
'a 50-50 chance' becomes 'evens' (I've seen this before).
'o' put after 'evens' is 'EVEN SO'.
(Other definitions for even so that I've seen before include "in any event" , "however" , "'Nonetheless (4,2)'" , "'Despite, still (4,2)'" , "anyway" .)