I just read Mangatstream version, OMZ melted away and became the Hilt of the Flaming sword. After he'd become the hilt, he invited Ichigo to take the sword. In Effect it seems he has poured his own power into the mix (voluntarily), and all of them are now Zangetsu.
I wonder if the Three Inner Spirits (Two?) will still be able to speak independently or whether the fully merged like Tensa Zangetsu did with Hichigo?
Really like the story.