5dimes doesn't refund money on players dropping on futures....unless they have changed something within the last year. It doesn't sound fair, but they are just protecting themselves, as when one person drops, value on the other players increases.
For example, if you heard Tiger was injured and might not play, you could loadup on mickelson at 8-1, then if Tiger did drop out, Mickleson's true odds would drop down to 5-1 and you have value with Tiger not in the field. Books hate it when you have value, so to offset this they will collect on Tiger bets placed before he withdrew. No harm, no foul for the books.