How about instead of hirelings they're simply a friendly mob that occasionally visits and helps out your quest as if they were another warrior dropped off and are simply stopping by to aid you. This can be a mob that you could find dead or fighting other mobs in the game.

The devs could put in items that can be interacted by the friendly NPC''s, an NPC bed, or other stations...there would be no promise of the NPC player, these npc would have a mind of their own so to speak.