Workers have too high priority for collecting items
Sorry, there supposed to be a video demonstration, but unfortunately OBS captured only sound and a static image for a reason. :(
It was supposed to show a worker that refused to claim a perfectly safe area consisted of an enemy tile and enemy Archive. I battled it for about a minute, dropping it as close as possible to the entrance tile. Interestingly, it agreed to fortify walls if dropped near one.
Anyway, whenever a worker goes for 'collecting an item' as indicated by its activity, it's not possible to force it out the activity via conventional means, such as dropping near its designated area. They will always return back to that activity, ignoring even fallen minions a tile away!!!
I want to add that rescuing minions has the highest priority of all tasks.
However my guess is your minion didn't place a bed in a lair yet, in this case he can not be rescued.
Or your minion was died and was a corpse already, which are collected with much lower priority or not at all if you don't have a crypt.
Intelligent minions are unconcious for maximal 60 seconds before they become a corpse which can not be rescued.
Beast units are never rescued and directly become a corpse when knocked out.