I have watch the previous seasons. I hope you can still find a way to put back LEE JIN WOOK in the lead role for Season 4. He justified the role very much and it went as very highly anticipated series. He has the very strong appeal to make the series very commendable.
Why not make a twist. You have shown that he died but can you make the story like he only had a near missed shot, a grazed shot in which he survived at the latter part. You just need to show the world that he died and sent him off because he needs to catch the real culprit. Then add the romance together with LEE HA NA to make the viewers more alive. If that would be the ending, it was very sad and I wouldnt want to watch anymore the next season because of Lee Jin Wook and Lee Ha Na. He should still remain as Do Kang Woo to finish as what he started and to be involved seriously with Lee Ha Na. They do have a great chemistry.
I find Song Seung Heon too old or matured for the role. I would still prefer Lee Jin Wook if possible. Please make it possible for Lee Jin Wook.