Join Date: Jan 2008
Location: Tricoastal - London, New York, Silicon Valley
Programs: DL DM/2.5MM, 20 Years Top Tier on DL, UA 1K, AC E75k, MR/SPG Lifetime Platinum
Posts: 1,309
You should just call to ask DL about this, but I believe that since you booked a RT award, you will lose the miles and the taxes/fees for the return will be refunded... They will likely site the 72 hour rule from outbound departure as the reason for non-refund of the return miles.
Good luck.
TFD