This flag seems to say "Levery". I suppose that's the Engrish version of Reverie?
At the same time the manga had us assume Sabo was dead as well.
The manga had Luffy assume Sabo was dead. I don't think many readers thought he was dead. Lots of hints as said above (end of the post-war flashback, chapter 668 cover page etc).
! He's stronger than I thought.