"The question verbiage insinuates an ING foul that occurs in the EZ will result in a safety-whether or not the penalty is accepted."
I think this is the point of the entire question. In NFHS, when a passer intentionally grounds the football, it's treated as a running play. In other words, the succeeding spot is the point from where he threw the ball. In this instance, the result of the play is a safety either way. If B accepts the penalty, then we have an enforcement spot in the EZ, which by rule is a safety. If, in the highly unlikely event B were to decline the penalty, we still have A in possession of the ball behind his own end zone, with him forcing the ball there. Therefore, it's a safety either way.