I don’t get your remark. If you have a Saver Day Pass bought at a reduced fare (not matter what you have chosen as reduction GA, Half Fare Card, etc.), you must be in the possession of the Swiss Half Fare Card; otherwise it is not valid.
If you do not have the Swiss Half Fare Card, and you are not considering buying it, then you have to refund the Saver Day Pass and buy one at full fare. Only then, your Saver Day Pass at reduced fare will be refunded.