Did you battle the demon?
If you battled the demon successfully, you won IWD. Only thing you can do now is export your characters to HoW and start the expansion, but that begins in a whole new area, in Lonelywood.
And there's no way to leave Easthaven once you get to it. When you face off against Rev. Poquelin in Lower Dorn's, that's the signal for the endgame sequence...there's no going back to anywhere after that other than Easthaven.
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