I didn't check those two (DL & NW) specifically prior to my previous reply as I don't think it is generally a good idea under any circumstances (as I noted). In this specific case, however, it is worse than that. It does not appear possible. Neither DL nor NW are listed in the WebFlyer.com Mileage Converter Tool as a source which means that the miles don't come out of those programs.

Even if DL becomes worse than it is - and the speculation on that front is truly speculation at this point - something as significant as a 90% devaluation (drop a zero off the balance) probably isn't worth it. Even if the program sucks you will likely still be able to find something to do with the miles in there.