I'm not sure if it would be too hard to implement, but I also like the idea of some sort of in-game hirelings/henchmen, but I would tend more toward them being NPC followers than to them having to be paid for.
At Level 10, it's conceivable that a character has earned themselves enough of a reputation as a heroic rat and earthworm slayer that lowly NPCs might be anxious to join them in their quest to rid the land of slightly larger rats and worms - perhaps even a dreaded gully dwarf or two.
If these were limited to one per person, counted as a member toward the maximum group size, and were limited to zoning only, I think they could prove helpful in rounding out groups when no one is online, while still not replacing the experience of real grouping when there are enough people on.
These could be available either from the Inn or from a nearby room bar, and be available in a few of the less complicated guild choices ( cleric, druid, warrior, barbarian, thief, & mage), be given training equipment to start, but with the option of equipping real gear, and have level scaled skills training and spells (all guildmaster spells, no book/charm/tablet spells), and have a static mid-range abiliity score array, depending on guild choice, they could be very useful without breaking the game.
They could disappear if the player dies, recall when the player does, and instantly drop all items and quit service if the player attacks or is attacked by other players.
This would allow a lone cleric to blind/stab for experience, provide some mediocre bashing to help with a self-healing mob, or give a lone scout some cure critical wounds or a tank to get through the toughest few beasties in a zone, without breaking the balance of the game too much.
It could also act as a packmule, with the built-in risk of an enemy clan or random pker attacking you and making your NPC drop all your loot at their feet and run away.
I think that, with some testing to make sure they are power balanced, it would add a lot to the game for people that just want to log in briefly and run a zone, without necessarily taking away from anyone running real groups or upsetting the balance of clanwars.