What remainers do, eg accepting Brexit ultimately (4)
I believe the answer is:
stay
'what remainers do' is the definition.
'eg accepting brexit ultimately' is the wordplay.
'eg' becomes 'say' (both can mean 'for example').
'accepting' is an insertion indicator (inserted letters are accepted).
'ultimately' suggests the final letters.
The last letter of 'brexit' is 't'.
'say' going around 't' is 'STAY'.
(Other definitions for stay that I've seen before include "Remain; detain" , "Remain behind" , "Reside" , "Supporting rope; remain" , "Supporting rod" .)