There is no way to email ONLY THOSE WHO ATTENDED AND NOT REPLIED TO THE SURVEY without you doing some manual intervention.

you can do the following to email all those who did not answer the survey, but you would have to remove those classmates from the e-mail who did not attend the reunion (or just email those classmates, too).

Survey Maker, STATS link, Scroll down the page to the very bottom, click the "Show/Hide Members who have not responded to survey (681)" link. Scroll down the list and choose the "EMAIL NON-RESPONDING MEMBERS" button.