So it seems you can have a lot of fun with Living Vessel. You can make it so Osoyo can be the living vessel and occasionally control the PC again when they reach 0hp. I'll have to read deep into their motivations to figure out how to do it, but it seems there is a lot of potential here.
Yes! After reading this adventure I think that would be super cool! Hopefully there's more details on Osoyo's motivations in later books