I've been thinking: Before the MC dives into his memories, the silat attendant tells him "sister awaits" and points to an energy vortex that looks a lot like the Vestige. The Vestige was formed from spirits that lost their individual egos from lingering in the dream world after death. And Valravn warned Syla that her remaining in the dream world would be bad for her spirit. So is Syla a Vestige now? It would explain why she's nowhere to be found and only communicates in whispers, if she doesn't have the sense of self needed to manifest properly.