I think most here would also like to know how many miles DL gave you gratis to complete your reservation? If it was 2,500 you might ask for a few more. If they already gave you 20K that's a different story

To ask for 50K when they got the ticket issued is rather outlandish and even if the CSR was open to giving you and extra 5K they wouldn't as it would have probably insulted you further.