How do you handle apprentices of player magi in your saga?
Who plays them when they're undergoing their apprenticeship, and how much statistical detail do you give them?
What happens to them once they complete their Gauntlet? (assuming the master character is still very much an active character)
For sagas of less than 10 years duration, this probably isn't an issue or hasn't come up. If that's your situation, what are your future plans for this?
In sagas where we have had apprentices, they were written up as full characters, played by the player of their parens. Once they completed their Gauntlet they left the covenant and became NPC members of other covenants. That said, I recall once when the magi visited a covenant where a former apprentice was a member, I handed that character back to her original player along with some notes of what had happened to her in the intervening years and what she knew about the new covenant, and let the player roleplay her.
My preference is to enforce a cross-fertilization of sorts another play playing the apprentice. This requires a fair bit of OOC discussion as the relationship isn't necessarily cordial depending on the circumstances of the apprenticeship. Some parameters need to be established so that one player doesn't feel like he's being degraded, though his character might be, by performing certain duties. If both players can laugh and enjoy the scenes when they conclude, then it's good. If not, something has to change.
Right now in Bibracte we have three apprentices in play. One is actually at an allied covenant, and two are at the player covenant. The apprentice at the allied covenant is a PC, his original master left the saga, and he's drifted aimlessly for a few years (that's my story and I'm sticking to it). I think the player has the goal of integrating the apprentice into the player covenant at the end of apprenticeship, but we're several years away from that point. At the player covenant, the apprentices are fresh, about a year so into things, so we'll see where things end up.
We have two apprentices, one of mine, who starts the apprentice at 16, and my magus (linea Trianoma) plans to to give her a lot if freedom during the apprenticeship, and one that starts somewhere below the age of 10, whom that magus will give a more sheltered and restricted life.
My apprentice is played by another player, and will see quite some screen time, the other might tag along very occasionally with the other wizard, but will hardly be of any interest. When it comes up, this apprentice will be played by the player of its magus.
At 16, you can have a somewhat rounded character, below 10 this will be a lot harder, and if you won't get a lot of freedom, there is not much play to it. It depends is my conclusion.