I've been thinking about it too. I haven't started a campaign yet and often play one shots with a cousin or two who don't know the rules very well, so I "play" some PCs and DM but there's always some party roles missing (like a party with no defender or leader) and it's hard to keep track of all the monsters and two or three characters at the same time.
So I'm contemplating stating henchmen as per the NPC rules: no small class features, no feats, no magic items, no big choices to make. Problem is, they only have 1 healing surge per tier, wich is not acceptable when you're hiring a defender.
Also, how do you make challenging encounters for a party with both PCs and NPCs? We know they get to keep the loot/XP, but are NPCs supposed to be counted as party members when designing encounters as well? I don't know if they are as versatile and powerfull as a regular PC with all those powers (heroic NPCs have less skills and only four powers: 1 at will, 1 utility, 1 encounter and 1 daily), so I'm not sure a party of (5 PCs) and a party of (1 PC and 4 NPCs) are equally effective.
One solution would be increase their Healing Surges per day up to their original class, or maybe 1/2 or even 3/4, so a hired defender wouldn't be a total meat shield but could do his job. As for powers, since I'm aiming for fast play, I don't want more of them - I'll just have to playtest to see if those "free" bonuses NPCs have are enough to compensate all those small class features and extra power choices they don't have.
As to handling mercenaries in game, I'd only let a character hire one if the party has less then 5 players and there is one role missing, and never more then one hireling per role - the goal is to provide a balanced party, not meat shields for the wizard. And there probably should be a penalty when you "let" you mercenary die. Maybe you cant hire again until you level up (it hurst your street credit) and until then, XP will still count the dead merc. You can still raise him though...
I think I won't track their XP per se, they will level up when PCs level up. They will receive their share of the gold, but never magic items (Quick idea: maybe the hiring cost would be like wealth per level, PCs would have to pay that sum in gold, maybe in three payments, to have an NPC follow them around through the course of a level, then adjust a new price at each level up, and I don't need to adjust the treasure every encounter)
Anyway, that's just what I've been thinking for my future games.
Let us know how you handle it.
