It won't work for everyone's table, but this is what happened at ours once.
It was early in a long-term, two-year campaign...I think it might have been our third or fourth gaming session? We were just getting started. The party of five, 2nd level characters were investigating some strange goings-on in a mysterious forest, and ran afoul of an ogre. What should have been an "Easy" encounter turned into a massacre: the party's cleric was knocked unconscious by a lucky dice roll, and then a combination of bad death saves and careless friendly fire finished her off. (But by golly, the wizard got to kill that ogre I tell you what.)
After the battle, I called a break. Everyone got up to get some snacks, stretch their legs, etc., and I chatted with the player. I asked her if she would like to keep playing her cleric, or if she would like to roll up something else. She said she wanted to keep playing her cleric, if possible, because she had spent so much time on her backstory and portrait and stuff (she even had a family tree). So we brainstormed for a few minutes, and I bounced a few ideas off of her. She picked her favorite idea and I ran with it.
So when we got back from break, we had the funeral scene. The party set camp, and as they were digging a grave, an old crone entered the clearing. She saw the body of the cleric on the ground and exclaimed. Such a pity, she said, for that particular cleric was destined for greatness and would have gone on to save many lives from a terrible fate. But now, alas, those lives would now be lost. She offered to raise their fallen friend, in exchange for a favor...but wouldn't give any further details about what that favor might be or when she might call it in. They agreed, and the crone raised the cleric from the dead. Then the crone (actually a powerful hag) vanished. From that day forward, every character in the party except the cleric noticed that their own shadows had been replaced with the shadow of the crone.
I never ended up calling in that favor; the campaign ended after about a year when I moved away. And honestly, I didn't really have anything planned for it. I just wanted a way to bring the cleric back in a way that would be memorable, and wouldn't be abused in the future. (And yes, I wanted to toy with them a little, make them paranoid, and remind them every now and then of the debt that would someday come due.)