With our knowledge: chances are Londo would be dead, yes (or rather the Drakh, since they wanted their revenge on specifically him, would have tried to get the keeper on him sooner). With Sheridan's, Delenn's etc. knowledge? Londo actually is rather good at keeping dangerous secrets. I'm not sure how much they know about how things went down on Centauri Prime and Narn, but G'Kar mentions his deal with Londo when greeting Garibaldi in "Epiphanies" so I'm assuming the broad outline is common knowledge on the Garibaldi-Delenn-Sheridan-formerly-Ivanova level at least. Meaning: yes, Londo has a temper, but he's also familiar with keeping a poker face when dealing with a crazy despot. (Oh, and then there's the relationship with Morden which wasn't exactly super secret after Londo was one of the people who asked for his release in "Shadow of Z'ha'dum", granted, but that was still a good while after it happened. And the late Refa would also be able to testify to Londo's ability of keeping lethal secrets. Ahem.)