Link I think the Forgetting is a very good idea. Youll have to work it out as to who and how the Hero is trained to regain the magic ability. you could make it to where this is really the first quest or just an early one. Once the Hero gains the use of magic it will give say the "tribal elders" a strong insight to the fact that he really is the The Chosen One. Now If he has his 2 friends go through the portal with him they could also learn the same thing of you could have to do Quests for them to also receive abilities. One could be a cleric and the other a theif or something like that. or just highly skilled fighters. vary they quests that they can undertake and you allow the user to change things up.
I think this could be like a family tree type thing. Theres the first Branch and what the user decides to do with his first character in a way manipulates what the others can do. If the main character decides to undertake the mage quest then that eliminates the possibility that other others can do it too. one would then be able to learn the art of the druids for example. or clerics. or theives. if you include some bg2 type classes 3 guys with the ability to choose what they become would really make the game replayable.
If the user changes one thing on the tree it changes the game entirely from that point on. Maybe not drasticly but enough so that you can really never play the exact same game twice. This is the really difficult thing to decide on. its not like bg2 where you decide what you are BEFORE you go through the portal. The PC has to BECOME what will shape his destiny.
Then of course, you can also add the types of NPC's that you need to balance out the party. Maybe even add instructors that will accompany the party t okeep them alive long enough to get to where they can survive and then say " Ive taught you all i can. My time with you has come to an End." Only to have these instructors rejoin the group near the final battle. Is one a traitor?? Did he really teach his pupil everything he knew???? My bet is that he didnt. But the pupil learned some tricks that hadnt occured to the instructor/ traitor. Hero wins. and gains more power for killing the instructor.
You could play with this idea forever. Dont be in a rush to get it done. Any writer will tell you that it takes almost as long to outline the story as it does to actually write it. Keep in mind that if you rush it you will surely screw up and leave something out. but by the same token if you try to do too much detail you can still screw it up just as bad.
Look at the Wheel of Time series by Robert Jordan. It could have been a really good story but he spent too much time describing Guiled this and Guilded that, He even talk about how they had Guilded fish at an inn one night. i dont think he knows that guilded means Decorated with gold trim, basiclly. So they had gold laced Fish??????? gimme a break. he got too caught up in describing crap and forget about telling the story. Who really cares if there is gold enamel on a door??? whats the story line Mr Jordan??? duhhhhhhhhhhhhhhhhh
oooops sorry kind of got away from me there LOL
anyway Link get back to me on thar and let me know what you think. take it easy.