Battle your enemy (here Damian) with the same weapons ... !
Damian & Ygerna were Soulforged, but not in the way Zandalor /the Divine known the outcome ... (right?)
So why not make a plan together with Zandalor to set a Cursed Soulforge on the Divine ?
The Divine try to kill Damian up close and personal ... IF Damina kills the Divine he cursed himself and so he's Soulforged with his most important allies, his most gruesome Black Ring generals (or whatever), thanks to the Cursed Soulforge Spell Zandalor used on the Divine.
With this plan the player has at least more than 1 way to defeat Damian and the Divine is playing a very important role !
Maybe turn around the roles? Let the "protagonist" try to kill Damian and the Divine go to kill Damian's allies ? Let this possiblility up the to the player for and extra way to make an end on Damian's forces ?
Kill all his allies (or at least some of his most gruesome ones) and Damian's is no longer !
Storywise :
Divnity III's story starts with the Divine and an the last of the Dragon Knights.(who killed Ygerna at the end of Divnity II)
Zandalor's first step in a great plan require some sacrifices :
the Dragon Knight's powers must strengthen back the Divine after his long period of "captured in a cristal" ... This is of course a great honour for the Dragon Knight. Then the Dragon Knight becomes back a very weak person and start his/her Journey (level 1) with his/her counsellor that is the Divine .
I don't know if Larian is planning to have "dragons" in Divnity III ? If so it can give Divinity III an extra dimension, but without dragons it's also possible to make a great RPG (I believe).
Maybe the Patriarch plays in DIII a more important role ? Why not . Could be fun .
IF the player/gamer loose his new hero it's over and the Divine must do the rest (idea) !
OR the Divine chooses another "person" (one of the NPC's in the game can be upgraded to a playable character ?? -just another idea !)
This all plop up in my mind on the moment, not sure it's possible and not sure if these are good ideas at all !
Just some "ideas", not more or less