This is late and will amount to absolutely nothing, but:

1) Redcloak will destroy the phylactery. I don't think there's any living character that hates Xykon more than Redcloak - not even Roy - and the symbolic gesture of ending Xykon's immortality (his greatest fear) is probably the sole emotional concession the story will give to Redcloak, as it's essentially him 'revoking' the choice he made to help Xykon become a lich decades ago. Other than that, my adjacent prediction is that if Redcloak dies, he will go to his god's plane, but none of his family will be waiting for him.

2) Vaarsuvius will survive. If Miko's death is the story of a lost possibility of redemption, then Vaarsuvius' is the story of how one might dedicate the rest of their life, goals, and happiness to make wrong right. I think it is more narratively rewarding to see how Vaarsuvius will climb the moral hill, as opposed to making the decision to climb it and promptly dying before they can embark on such a journey. Also, V will adopt Mr. Scruffy and Bloodfeast; both animal companions get along very well with Blackwing.

3) There will be a 'flash-forward' while someone (Elan?) is voice-overing in the present, and we will glimpse a died-naturally-Roy reuniting with his brother. If anyone's doing voiceover in the end, it's Elan.

All three predictions are pitched with varying degrees of confidence, which present as my left foot, my favorite pair of shoes, and five dollars. Respectively.