Just discovered this thread and already put much of it elsewhere, but this would have been my ideal course for a 100% Happy End:
The enriched infernal iron and maybe some Canian ice from Helsik help stabilising Karlach's heart while the freed Gondians look for and find a solution between the docks and Reunion Camp
After losing the Emperor to the Absolute, Omeluum (informed of the Emperor's betrayal by Withers, Jaheira or another companion after the strike team left for the Upper City?) reluctantly agrees to wield the Netherstones
Karlach can enjoy her mutton chops at Reunion Camp and Happy gets to live