Welcome to FT! The other posters are correct; there's no way to get miles without actually traveling, but cancelling the ticket will at least likely result in some credit for future travel, which is better than nothing.
This is assuming that the tickets are normal DL issued tickets for USA originating travel. Some exEurope tickets can be truly nonrefundable and I think the same might be true for the new E fares as well as some consolidator tickets and other unpublished fares. Also, if they were purchased through an on line travel agent like Expedia, the situation is a bit different in that you must deal with them rather than DL.