I had a dream I was at the airport after taking a short ride on a trans Atlantic flight from one gate to the next (one of those things that makes sense in a dream) and I saw a dude from my area who was recently killed. I told him about this and he was basically
about it. He stated that it was unfortunate but that was in another realm and it didn't affect him in any way, shape or form.
Then his deceased doppelganger appeared and started chasing him. He knew it was a life or death struggle. The doppelganger was like, "I'm not trying to hurt you. I just want to talk about your soul. There might be a soul in there!" So he chases dude and touches him but the guy manages to get back up but not for long. I told him if your doppelganger touches you it's not good. And it wasn't. He couldn't run as fast anymore. The doppelganger caught him and gave him a bear hug and they both sank into the ground screaming as another version of himself dressed like a Catholic Cardinal watched on sadly.
I say all that to say who knows why people disappear without a trace. Yeah, most are murdered or just die and are never found. A small percentage I think have some sort of supernatural origins.