For the record, Straczynski is 67. So, could be good for a couple of decades, might be dead tomorrow -- much like many of us.
Londo and G'Kar were main characters whether or not they were "lead" characters would depend on the definition. One of the side line stories I really liked was the telepaths. The whole idea the Vorlons were responsible for their existence and the dominos which fell in human society because of it.
“Extinction is the rule. Survival is the exception.” -- Carl Sagan