Even experts can be defied by experts. It wouldn't be the first time Damian has thwarted Lucian (as he wasn't meant to be able to escape through the rifts for a start). Lucian's entrapment happened around 8 years after DOS2, towards or at the end of the great war.
I'm not sure how it couldn't make sense based on your argument.
Well, it's wasn't Damian's plan to escape Nemesis, but Asmodeus's, boy just "played" his part as a DK. Overall, Lucian maybe a real idiot, but Damian, considering what we saw from him in Divinity Dragon Knight Saga, just a complete moron, cartoonish villain. Story writing in Divinity II was the worst than in any other Larian game.
So yeah, in regards to the question of the thread author, Lucian double "death" is absolutely ridiculous.
