Hi, I'm Jina! It's always hard to say anything to someone who lost their loved ones. I would say like this to my friends in this situation "힘내, 좋은데 가셨을 거야.." : Hang in there, They must have gone to a peaceful place. "하늘에서 너 지켜 주실 거야" : They will take care of you from the sky. "이제는 편안하실 거야" : They must be relaxed now *These are for when older people passed away* If their friend's or younger people passed away, you can say "힘내, 좋은데 갔을 거야" "하늘에서 너 지켜 줄 거야" "이제는 편안할 거야" in same meanings. It was hard to explain in English for me but I hope you understand and it will help you (:

"고인의 명복을 빕니다." Pray for the bliss of the dead. "상심이 크시겠어요. 고인의 명복을 빕니다." You must be in great grief. Pray for the bliss of the dead. This is a general formal phrase to anyone who lost his/her loved one.

Thank you a lot! These are good expressions to write!

More casually to a friend who lost the loved one that is older: 마음이 많이 아프겠지만 좋은 곳으로 가셨을 거야. 힘내. 많이 슬프겠지만 기운 내. 평안한 곳으로 가셨을거야.