On June 28, the Sanders campaign solicited donations "to help our delegates come to the Democratic convention so we can have our entire political revolution represented next month in Philadelphia."
The Sanders campaign knew at the time of this solicitation that an endorsement of Clinton would make presence of his delegates at the DNC unnecessary. Hence, funds were solicited under false pretenses and should be refunded. Let Clinton and her backers pay for any delegates who still want to attend.
Why is this important?
We would not have contributed had we known an endorsement before the convention was being considered. We want our money back.