first, it was a Delta/Itrepid plan...(the leasing company involved with some of the Skymark widebody aircraft)
second, DL undoubtedly knew there was a risk and probably a lot of money involved in the bid. The risk is because Skymark has very little presence at NRT so that would have to be built while there is a pretty big barrier between connectivity for US and Japan flights at HND. DL has been pretty successful at arguing that the US should not allow any significant flights between HND and the US at times which would provide connectivity because it would harm DL's NRT hub. DL's decision to maintain 2 HND flights and then give up SEA was undoubtedly driven by its desire to ensure that DL maintained the leadership size in the US-Japan market as long as there was any threat to DL's NRT hub.
third, DL's bid could have been a "spoiler" bid.... just like with JL and Skyteam, it might have been a long shot but it increased the cost to ANA.
fourth, it leaves Japan in the policy quandry of having a very unbalanced domestic market again since ANA just got a disproportionate amount of slots compared to JL at HND and this will further aggravate it. This is bad news for JL as much as some would like to try to present it otherwise.
DL has been working for years to minimize connectivity over Japan while reducing the cost of doing business in Japan. The new 333s can fly most of DL's NRT operation at a much lower cost and the 359s can do JFK and ATL.
DL likely knew its bid for Skymark was a stretch which is why it acquired a stake in China Eastern which will likely yield better results at a lower cost.
Further, DL labor including DL pilots saw this transaction as a risk to their jobs even though it wasn't clear how it would work.
DL is in the position now of continuing down the same path of growing service to destinations in Asia beyond Japan nonstop from the US, reducing capacity to Japan to remove connections while maintaining its share in the local Japan-US market, and increasing its cooperation in other markets.
I predict we will see at least one and possibly two more nonstop US-Asia flights for 2016 with TPE likely near the top of the list and the elimination of NRT-TPE.