Mystery surrounded the whereabouts of Bashar al-Assad, who was no longer in Damascus when rebels captured the Syrian capital on Sunday, ending more than five decades of his family’s rule.Two senior army officers said Assad had boarded a plane early on Sunday in Damascus for an unknown destination.Russia, one of Assad’s closest allies, confirmed that Assad had left Syria but did not say where he was, including whether Moscow had given him refuge.“As a result of negotiations between B. Assad and a number of participants in the armed conflict on the territory of the Syrian Arab Republic,…