1) Start crediting the rest of your flight miles to DL, realize you lost 15K EQM this year for no reason. Given the fact that your wife is DL elite as well or will be, when you vacation, you'll probably fly DL or SkyTeam more than anyone else - it sort of make sense for you two to be on the same program.

2) If you've got between 25,001 & 49,999 miles, you're a Silver in DL's eyes. No difference between 25K & 36K.

3) Get a NW credit card to bump the 15K to 25K (assuming that's all you've got in your NW account) - get a free ticket somewhere.

4) Maybe, if you're lucky, you can send DL your statement from NW & explain to them that you screwed up & you're not sure why you did what you did - maybe you didn't realize that a NW could earn DL miles - or, maybe your "secretary" entered the wrong FF number in the PNR - any number of reasons - and ask if they'd be willing to hook you up with DL Gold given the situation that you're in & that you actually have flown that many miles & would have creditted it to DL had you been able to. It may not work, but it never hurts to ask a financially strapped airline if they'll allow you to be a loyal customer.