ThatMG wrote:if you argue that hexrifle effect does not go off then your fnp does not go off
simple

Yes, FNP does not go off TWICE. It only does it once and exactly at that moment the whole injury along with any effects like loosing wound, removing model, hexrifle and FNP are all ignored. So what FNP is ignored if there is no "not ignored" wound to take care of.
Just like Junk said. Those rules may go both way. You need to talk this through with your opponent and maybe roll off.