I dunno. Sinclair or Valen I thought was pretty much dead. Note that he has never met Lorien nor has he ever come to understood the ancient conflict of the Shadow and Vorlons. As far as he knew in that time, the Shadows were an ancient enemy that had to be stopped. And it was his destiny to stop them in the past.
<table bgcolor=black><tr><td bgcolor=black><font size=1 color=white>Spoiler:</font></td></tr><tr><td><font size=2 color=black> And part of his motivation to go back in time was to find Catherine Sakai, his lost fiancee who accidentally enter the time rift while on a mission to prevent the Shadows from exploiting the rift before Draal's Great Machine could exert full control over the time rift.</font></td></tr></table>
The above is exerpt from "To Dream in the City of Sorrows". If any material is cannon, its this book because it was written by Katherine Drennan, the beloved consort of our beloved writer JMS.
And if what the comics say is true, Sinclair did find Sakai and lived happily ever after.
This was also implied in the epilogue of the book.
Back to the original question, it is up to debate what happened to Sheridan himself. My interpretion is that he DID die, but his soul or mind travelled with Lorien to heaven rather than experience all the unpleasantess of leaving your physical body. For all we know, when Lorien sez
Beyond the Rim he not necessarily talks of a mortal plane. Maybe it's a place between heaven and earth (pun intended) where all the First Ones have gone to leave space for the younger races. Lorien said "we have been waiting for you". It could mean Sheridan elevated into a higher form of life or just have a final meeting with the First Ones before completely leaving the mortal realm. My personal opinion? He is dead. Let's leave it at dead. If not, Delenn will be one lonely soul in Heaven because she's the only one who actually died among the tree.
Thinking of all this makes me wanna cry. I still say Sleeping in Light is the best episode I have ever seen. May Rangers be just as good though with a different storyline. I hope JMS doesn't carbon copy his B5 artwork though given his creativity, I don't think so. (Touch wood)
Take care of yourselves, people of America.
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May the light of the Buddha, Dhamma and Sangha protect you.
May you all be well and happy, free from suffering, free from sickness.