Wow. Thank you very much for sharing this story.
Honestly, this is a bit surreal. I always figured this would be one of those mysteries which never gets solved. Where we have some theories, and we're almost sure of the answer... but its really all just speculation by people who don't know, while those that do will never tell. But now JMS has. Kudos to him, and to O'Hare for wanting/allowing the story to be told after his passing.
As for O'Hare himself, I though he was brilliant as Sinclair. I much prefer Sinclair to Sheridan and O'Hare's acting has a lot to do with that.
We can only speculate about what B5 would be like had Sinclair been the central character for all five seasons, but I'm certain it wouldn't have been any less spectacular.