In effect, you have three mana dump spells to end the game - but two of them are the only non-blue spells you run in the deck. In addition, damage prevention effects are more common than effects that prevent card draw. I'd suggest cutting
Debt to the Deathless for
Fascination. As
Fireball only requires a single colored mana, you can use it as removal in a pinch as long as you have a
Pili-Pala.
Debt to the Deathless has too restrictive a mana cost to be usable in a pinch - either you're going off and the game is over, or its uncastable.
Fascination effectively acts as a second
Stroke of Genius - in fact, its almost a strictly better
stroke of genius (requiring double blue in the mana cost, which isn't an issue for this deck), that has a mill option to get around effects that prevent drawing additional cards.
I'd also consider something like
Trickbind, to put a stop to some decks that go off at instant speed. You may be able to cast your
Fireball for infinity, but if your opponent can throw their win condition on the stack after it, you aren't in great shape.