When you answered about "an uncertain[t]y that is apparently laid to rest...," only the inclusion of "apparently" left a margin for considering your questions as being more than rethorical ennumerations.
The last lines you mention are:"And then the masquerade draws to a close. The bald little prompter shuts his book, as the light fades gently. The end, the end. They all go back to their everyday life (and Clare goes back to her grave) — but the hero remains, for, try as I may, I cannot get out of my part: Sebastian's mask clings to my face, the likeness will not be washed off. I am Sebastian, or Sebastian is I, or perhaps we both are someone whom neither of us knows."
and in these we find hints of authorial interventions, similar to Bend Sinister's, and a whiff of "As You Like It" (the world as a stage).
So, the mystery related to the last sentence remains, for V. invites us to remember that "what you are told is really threefold: shaped by the teller, reshaped by the listener, concealed from both by the dead man of the tale."
For me, as stated before, Nabokov had great ambitions for Pale Fire, the poem, and was unsure of its reception (nothing less than "great" as a final verdict?). Although his style incessantly shifts from parody to self-parody, when his mystical and Romantic inclinations become the chief subjects of his mockery, he never gives up his attempt to convey otherwordly intimations - and these abound in PF,poem, in a serious vein.