Possible Spoilers!
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Yeah, I have thought about this myself. I never allowed anyone in my party (except for Imoen in the beginning; somehow she would come in my party whatever I said in the first dialogue

But as soon as she was in, I kicked her out) I killed Valygar after searching for an option in his dialogue box that would give me the opportunity to send him to Planar Sphere. As I am Neutral Good (IIRC) that wasn't roleplaying very much, but it had to be done to keep my 100 % solo idea.