Getting rid of the passenger requires giving up the coin, and since the PC in question is a Sorcerer it would also require her to give up all her magical power.
Am I getting all that right? Am I missing anything?
You don't need to get rid of your magical power. Harry didn't. He just changed the "shadows" perspective on life. It was Micheal who told Harry he had to give up his power.
It is one theory. That's it.
I am not so sure I would agree that the bound Denarians don't try to 'force' their desires on someone. As we've seen from the novels, there are two basic camps amongst the Denarians. Some of the members of the order are known by the name of the host (Nick, his wife Tess, and their daughter Deirdre...) while others are known by the member of the Fallen associated with the coin the host picked up. The basic difference between the two camps is that members known by the host's name are known that way because the host and the Fallen have a partnership. The others whom are just known by their Fallen are they way because the Fallen personality has completely subjugated the host and taken 'the drivers seat..."
Given that some of the Fallen were in control, it does suggest to me that, depending on the sort of personality the GM wants the Denarian to have, there could be internal battles of will between the character and the onboard Denarian. If that is the case, then something like Demonic Co-pilot could model the situation rather well.
-Cheers
But that could be simply the result of poor choices on the persons part. Look at sanya. He had magog but he was still sanya. Now look at magogs host in SmF. He's just magog now. Probably because he wasn't careful to not give the demon any leeway. Take too much from them, under the wrong conditions and just like the Fae, they will own you heart and soul.