So, after thinking about different ways to continue the campaign through after part 6 (and looking through various ideas), I've thought of a way to have my players fight Kavazon in all his glory.
Mythic Tier.
I figure, after the PCs grab Serithtial, they get filled with mythic energy and gain their first tier. Obviously, this changes some of the book 6 enemies' stats somewhat, but that's not terrible for me to fix. After they fight Ileosa, they can gain their second tier.
But their victory is short lived, because, at the beginning of the proverbial book 7, Laori comes to the PCs, grievously wounded [even though we aren't even close to this part, I know my players will side with her]. She tells the PCs that a rogue faction of the Brotherhood has stolen the remnants of Kazavon that the Brotherhood have so far collected, and are planning on reviving him with as many pieces as the they can (i.e. the more pieces of him, the more powerful he will be when he is revived). The PCs should control the Fangs, and at the end they should clearly fight Kazavon in his human and blue dragon form, but I am a little stuck on the details.
Obviously, the PCs should be focused on finding the remaining pieces of Kazavon, but I'm not sure where the pieces should be placed, or what kind of challenges the PCs should face to get them. I would like them to be Mythic challenges, and, if possible, it should be some sort of race against the rogue faction of the Brotherhood. At the same time, I'm not sure where the remaining pieces of Kazavon should go. Basically, I was wondering if anyone had any ideas to complete my skeleton campaign.