Looks like Delta will stop flights from Guam to Japan but not from Saipan to Japan. Sounds very strange but I guess people can fly from Guam to Saipan to Japan. Not sure of the reasoning but some sources link it to the threats from North Korea. Per nasdaq.com:
The above route had become all the more unfriendly for air travel, thereby denting Delta’s profits following North Korea’s threat to attack Guam. The threat and the resultant tensions had caused low-cost carrier Hong Kong Express Airways postpone flights on the Japan-Guam route until next summer. North Korea has, in fact, fired couple of missiles over Japan.
In fact, Delta’s decision to withdraw service deals a further blow to the already struggling tourism industry in Guam. Travellers from the Land of the Rising Sun have mostly avoided Guam, following the missile threats. This is further substantiated by the fact that Japanese cancellations accounted for most of the 7000 + tours to Guam that had been called off in August. The tours were of varying nature ranging from educational trips to those for business purposes. The cancellations caused Guam’s tourism sector substantial losses in August.
So we’ll see what happens. Regardless, I still would rather fly JAL.