I can relate a couple experiences of “losing” a pack:

First was in some fairly open, flat (featureless) woodland. A pleasant day, but quite a gusty wind rustling the trees.
A member of the party headed away from the small group for some Number 2, and because of the open nature of the ground, went quite a long way, leaving the pack behind (of course). When finished the business, the person stood up and found themselves disoriented. They could not see the main group and weren’t sure which way to go ! After some time we realised it was taking too long, and walked in the direction - we knew only the basic direction the person headed in. Although we were calling, then blowing our whistles, they could not be heard effectively because of the wind (and a bit of panic too I suspect). Eventually they heard us and then saw us, so the lost member was found and all was well. But it was a lesson on many fronts, including the need for an “on-body” kit. This experience was with a competent adult who was simply not thinking when heading off for a very mundane task.

-Disaster happens when you least expect it, so don’t get caught with your pants down !

Second time was a little different, (actually this was a close friend of mine), was camped in the wilds, but not too far from the vehicle (half day walk, about to head off for a few days). They pitched camp, had dinner and put stuff back into their packs and put the packs into the vestibule of the tent. Next morning one of the packs was gone and there were several inches of snow. The looked about, but couldn’t see any sign of the pack or how it had been removed from the vestibule, and no tracks in the snow. A mystery ! They reported the loss to the ranger and police and several months later the pack was found by some hikers in the general area where it was lost, but empty of contents. The only explanation anyone could come up with was that an animal dragged it off in the night. A bit un-satisfactory, but the end result was a lost pack in the wilderness.

They were with other people so there was equipment available etc etc, but had they been several days into a walk it would have been very inconvenient. Having told that story, I’m not sure that on on-body kit would have been helpful, but it shows that people (with brains) have lost their packs !