The preview episode 15 Descendant of the Sun showed one of Alpha team member go to see Mu Yeon at hospital. And Mu Yeon's face who was happy at first went dark after hearing what his said (we never heard what they were talking about).
I guess they want to inform Mu Yeon that Yoo Si Jin is missing or taken as hostage and they haven't heard any news from him.
There is two rumor of possible ending of Descendant of the Sun, the happy one and bittersweet ending one
1. Happy Ending - I read from Yibada
Some time later ... Dae Yeong and Myeong Ju get married. Mo Yeon attended their wedding but she did not see Shi Jin and she was disappoint. When she started to leave, Dae Young called her and told her the state of Shi Jin that time. Shi Jin was severely injured and almost died at that time. But even Dae Young did not know where Shi Jin went after it. Mo Yeon will not give up hope. Mo Yeon still follow the Special Forces who served in different countries.
After 2 years, Mo Yeon back to Urk, back to shipwreck again. From a far, Mo Yeon saw a familiar man standing there at sunset.
2. Bittersweet ending - I read from mskoala.
Shi Jin went again to the 'Mall' while he was on a date with Mo Yeon. Shi Jin re-assigned to protect the President of South Korea. Shi Jin success in protecting the President and instead, he received a lot of shots. So Shi Jin re-sent to the Hospital Haesung and Mo Yeon once again is the doctor who handled it. But this time it is not easy to save Shi Jin.
Shi Jin returned tease Mo Yeon who was crying as hard as possible to save Shi Jin. Shi Jin said that this is the sexiest phase Mo Yeon for becoming doctors. Shi Jin asks Mo Yeon stop trying to save him and he died on her shoulder.
Mo Yeon can not move on from the death of Shi Jin and their bitter memory, so she decided to return to Urk as Doctors without borders and live with Daniel and Yi Hwa. did not want to stay in Korea for the bitter memory.
Mo Yeon back to shore shipwreck and put the white stone to its place. She experienced 'morning sickness' there made her realize that she was pregnant with Shi Jin. Their baby is the last gift of Shi Jin for him to always cherish their love. While Dae Myeong Ju Young and getting a very happy ending. They married and had children
So which one is your pick?