Complex sentence: After he is diagnosed with carcinoma, Koyuki proposed to him and planned to have him embalmed after his death, but he had never sent in the marriage certification forms; as there was no relative to give permission, he wasn't embalmed.
Split into simpler sentences: After he is diagnosed with carcinoma, Koyuki proposes to him and plans to have him embalmed after his death. However, since he had never sent in the marriage certification forms and as no relative was present to give permission, he wasn't embalmed.