You can get gift cards from the medallion marketplace for about $1 = 100 miles depending on your status. In that way, you are pretty much even. You can use miles for hotel and rental cars on the medallion marketplace as well.

Will you friend be travelling on Delta before the cert expires? If so, keep the $250 voucher.

If not, trade it in. Use the miles for a gift card to somewhere you will use it or hotel or rental car where ever you like.