I think it's a mark of especially skillful storytelling when you let the audience know the shape of the story early on - even from the beginning - and you can make that knowledge actually work to enhance the narrative arc to make it more powerful. Londo's tragedy is actually worse because you can see all the bricks being painfully laid long after you know there's going to be a wall there. That little voice that says maybe it won't actually be so tragic as it seemed, maybe there's some mitigating factors I didn't see just makes the crushing doom more effective.

Also, I just want to say that I have mad love for the final episode, and I'm looking forward to seeing your take.