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Just thinking about Throne of Bhaal... spoiler!!
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In the beginning of Throne of Bhaal, when you've defeated Illasera, you will be automatically transported to your Pocket Plane, where you will have your little chat with the Solar.
If you do not have a party yet (start a new Throne of Bhaal game) or wish to change NPC's in your party, then you can use those fancy spirits (or whatever they are) to summon any NPC to the Pocket Plane, save for one. Aye, you've guessed it right: Yoshimo cannot be summoned. He's in the list, true enough, but if you click on him the spirits will say something like: "The person you are trying to get here is dead. He cannot be summoned."

To conclude: I do not think you can resurrect Yoshimo after Spellhold. IIRC he is removed from your party if he dies, and why would you even want him? He betrayed you (even if he had that geas cast on him).