I think that the nuclear bomb plot will either be resolved in the finale, or in the first two episodes of season 2. I can imagine, instead of resolving the bomb plot for the finale, something else, that's been hinted at, will take the front stage and throw the series for a loop.
See, in Babylon 5, we had a mystery from the pilot - which is what happened to Jeffrey Sinclair (the main character) at the Battle of the Line (the last battle in the Earth-Minbari war). The Minbari, who were winning the war totally and completely (they were 1000 years ahead of earth technologically speaking), come to Earth. During the Battle of the Line, the last battle, Sinclair blacks out for 24 hours. When he wakes up - the Minbari surrender. No one knows why. This is the big mystery.
We find out what happened to Sinclair at the Battle of the Line in episode 9, "And the Sky Full of Stars", and we find out why the Minbari surrendered in the first episode of season 2, "Points of Departure".
But the season finale, "Chrysalis", has nothing to do with this arc. It is instead, the pay off to a background sub-plot that's been going on for several episodes innocuously, and builds up to a huge pay off in the climax season 4.
I can imagine that the Yagamoto industries or Mr Linderman being such a catalyst for a completely different story, and that being the finale. With the nuclear plot being revealed in the beginning of season 2.