xkaliforniax

I only killed 3 and the one under the tool box spawned back in for me. I haven't gone back under the shed yet to get that 4th one. But I have done the battery cave, tool box twice now and the one under the rock. I just so happened to go by the tool box not too many days after the battery cave one and it was there again all of the sudden. I have not checked the others yet but plan to.

They added a recover backpack option in the start menu. You can do it for instances like this, once per load.