i have recently lost a few players in my campaign to new jobs... and have been looking into ways to keep the game running as the other players want to conmtinue. so far the best i can come up with is this..

after many years of d&d. i ported over the leadership feat as a talent ... basically  it will alow players to take on an additional character but they will only gain xp at a quarter of the speed of the actual player characters. i havent yet put a price on this talent but just wanting to know what people think??

It is a fun way to round out a smaller groups, provides your players with backup characters and keeps them involved, and works in just about any sytem, go for it.

Though I'm used to half xp, otherwise the cohorts can become useless.

half xp.... i can work with that but how much should the talent cost initally?

Since they aren't balanced into the system I would normally just give every character a cohort. It helps keep the "party" at a useful size and allows everyone to be involved in most of the interesting situations.

If you really want to charge for it...a lot. As an ability Cohorts could be more powerful than ANY single ability in the game, especially if they gain XP independantly. If they are a XP 'leech', only leveling up when the character spends XP on them when it makes sense, but if they level up on their own, that has the potential to be incredibly inbalanced. It would have to cost more than whatever their currently most expensive advance costs.

I have had great success giving players a 'secondary' character. It keeps things balanced, and makes DMing a lot easier because they are just standard characters.

I had a similar problem.  I created a simple system of spending allow Player Characters to spend 1 Fate Point (once ever, for now :), for either 2 basic NPC cohorts (meaning, a Novic Navigator, Novic Tech Priest, Hired Gun, Spy, Adept, etc.) or 1 Fate point for one advanced NPC (like an Orc, Ogryn, Eldar, Kroot, Oathsworn Bodyguard, Pirate Captain, Astropath, etc.) .  XP/Skill/Talent awards would be based on what actions that NPC did.  Meaning, if the characters and the NPC were conducting allot of boarding actions and succeeding, the NPC would probably get a permanent +5 to BS, or +1 Wounds.  These NPC's would also have 1 Touched by the Fate point to represent how important, yet minor, they are to the story line.

Of course, you can always allow players to roll up NPC's using either Dark Heresy rules or Rogue Trader (but remember Rogue Trader char's are considered 5,000 xp DH char's) for the cost of 1 Fate Point.  These are options, but all in all, it's about having fun.  So the choice is up to the players and the GM to agree and decide upon.

why make it that complicated?  Just have them roll up a secondary character.  After all you wouldn't have a problem with more PCs if there were more players, so why would there be a problem if each had 2 (or just those that feel comfortable with it)? 

Alternatively: either detail the important NPCs yourself or have the players do it.  Then if the need arises those NPCs can do things if so ordered by the PCs.  That's what the command skill, air of authority talent and other such things are for.  It stands to reason that any good captain will hire or train good officers.  Maybe have them progress but really slow at 1/5th or so of the xp others get.  PCs are extraordinary in the extreme.

Charging your players for something that should be there to begin with makes no sense to me.