Nominal leader would be sacked if he argued (10)
I believe the answer is:
figurehead
'nominal leader' is the definition.
(I've seen this before)
'sacked if he argued' is the wordplay.
'sacked' is an anagram indicator (sack can mean to plunder or destroy).
'if'+'he'+'argued'='ifheargued'
'ifheargued' is an anagram of 'FIGUREHEAD'.
'would be' is the link.
(Other definitions for figurehead that I've seen before include "bust from the navy" , "Nominal leader; carved bust at prow of ship" , "not as important as he looks?" , "may be bust" , "Nominal leader without much power" .)