In any case this has nothing to do with my gripe. My gripe is that losing the portal battle ends the 'find a cure for the curse' quest which is nothing to do with what is going on with this warning, or at least as far as I can see. Maybe I am missing something here?
It is the failure of the find a cure quest that annoys me not the death of Halsin or even the failure of the Art Cullagh quest. Am I to believe that completing the game by defeating all these major bosses doesn't not remove the curse because Halsin died? Who exactly is/was responsible for this curse?
Ketheric Thorm is responsible for the curse and sending Thaniel into the Shadowfell. Halsin is going through the portal to rescue Thaniel. If Halsin dies at the portal and therefore doesn’t rescue Thaniel, the curse can’t be lifted.