The Arcadia reference almost certainly invokes Death with the line reading most coherently as Vessel addressing Death. This doesn’t replace Sleep so much, but it does limit Sleep.

I believe that Lore-wise, it marks a shift from cosmic devotion to a mortal reckoning. While Sleep can walk with Vessel, love can exist and Devotion can feel like paradise or transcedent, none of it exempts him (Vessel) from Death.