This is my COMPLETELY UNOFFICIAL opinion:
I still believe they have the contract, however I think the contract is for a certain amount of dramas, that either DF picks and chooses (which would explain why they would go for the “trendier” ones) or ones that CJ E&M gives them. Viki got the license late on Pied Piper and apparently got the license for Memory – just a few days before premiere. It makes me wonder if DF decided to pass on it for whatever reason because they thought they wouldn’t attract enough viewership and didn’t want to expend the man-hours subbing it, so then it was available to be licensed elsewhere.
Again, this is purely speculation on my part, but I think you’ll generally expect to find most tvN shows on DF for the next couple of years. However, it’s nice to know Viki can indeed be a back-up if DF doesn’t pick up a tvN show.