Prize for Contest

We are coming to the end of an attendance contest which asks that the winner bring more than 5 guests to receive the option of one of two prizes. (The prize not selected is already planned to be a part of a fund-raising auction in November.) If there is not a person who fulfills this requirement, is it permitted to put both prizes into the auction? Or is there a "requirement" that a prize MUST be given away even if the
recipient has not achieved what was asked?

Thanks so much.
shirley43