Yoshimo questions (spoiler)

[Abecedarian]

If you have Yoshimo with you in the Asylum, can his betrayal take different forms? I assumed I would be fighting him at some point, but instead he did nothing until I completed the Asylum tour. Then, while the screen is frozen so Jon I. can make his speeches, Yoshimo just disappeared from my party list (along with all the equipment he was carrying) and Irenicus made a couple of references to the betrayal while Yoshimo apologized for it.

I had to go back to the start of the Asylum and relieve Yoshimo of all his stuff before he disappeared (so I could give it to Imoen)--hated to "cheat" like that but there was no way I was going to let him walk off with the various rings and boots which help a thief.
I assumed his "betrayal" would be more overt--in fact it's not clear to me what his betrayal consisted of, other than accompanying me to the Asylum and leaving. The real damage is done by Simon slipping you a delayed Mickey Finn on board his ship.

[koz-ivan]

if you brought yoshi along, you'll get a chance to fight him...

[Metatron]

Yoshimo will fight you eventually.
Additionally, you can safely assume that the entire time you've had him in your party he's been reporting to Irenicus on your movements.

[Yshania]

His betrayal is worth big exp after you meet his geas (spoiler)

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(as Jon I. leaves)

You need to pick up something from him and deliver it to a Temple of Ilmater....