What I do care about is knowing that Londo will never stop being an ally with the shadows until about 17 years after the events of B5, and only then after his world is trashed. He doesn't even have the opportunity to have a change of heart, which is all I want. Even if he ends up not learning his lesson, I atleast wanted the chance that he could turn from the dark path he set out on. Now, I know he definately won't. They were good, but not worth ruining Londo's story arc.
They don't ruin his arc; what actually happens is quite different from what you are assuming. That stuff is in the next two seasons (and a bit of stuff coming here in season three.)