Well, Sheridan's time travel seems to be a closed loop, same as Valen - Delenn warns him not to go to Z'ha'dum, but he went there because he was warned not to go there by Delenn. I'd go with just it's a lot easier and safer to ensure closed loops remain stable than to cause changes - and Zathras leaving B4 in 2258 would be altering the timeline, not keeping it as it was.
(For that matter - Zathras could be involved in a closed loop himself. It could be the only reason anyone thinks he'd die if they left B4 ahead of schedule is because Sinclair heard Zathras say that here - and maybe he warned Zathras of that later, and Zathras had no reason to doubt the One...)
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Date: 2009-06-02 01:18 pm (UTC)(For that matter - Zathras could be involved in a closed loop himself. It could be the only reason anyone thinks he'd die if they left B4 ahead of schedule is because Sinclair heard Zathras say that here - and maybe he warned Zathras of that later, and Zathras had no reason to doubt the One...)