[galraen]

I'm curious about you character, your post sort of implies it's a mage of some sort. If it is then for gameplay purposes you don't need Imoen. She'll probably be quite weak in relation to the rest of your party right now, but unless your character is a straight mage or sorcerer/ess then eventually she will be a much more powerful mage than Jan or your PC if he/she is a multi-classed mage.

As far as role-lay goes, Fable has it pretty well covered. If you're good then the decent thing would be to get her back to civilisation; depending on your definition of civilisation that could be Brynnlaw (the pirate port outside the Asylum) of all the way to Athkatla, which is quite a long trek. If your neutral then you could leave her to find her own way out, survival of the fittest sort of thing, or maybe take her into the party (difficult when you have a full party like you have, but you could tell her to join, then remove her immediately before actually joining up), then tell her you'll meet her back in the Copper Coronet. If you're evil you could just cut her throat or whatever.

Morally it is difficult because to pick up Imoen you have to strand someone else in Spell Hold, and not all characters can get out on their own, whereas, as I recall, Imoen can if you tell her to join then remove her as mentioned above.