What would have happened if Voldemort had won Priori Incantatem before Nagini had been decapitated?

Question

As wielder of an elder wand that belonged to Harry, during Voldemort’s Last Stand, there are two instances of Priori Incantatem occurring, back to back.

Basically, the current order of events makes total sense. Since Nagini was the last horcrux, when the body died, the fragment of Voldemort’s soul locked in it was released. This disrupted the first instance of Priori Incantatem, and Voldemort was now significantly weaker than Harry – so Harry won. Naturally, the Elder Wand’s killing spell was reflected back on Voldemort because of Priori Incantatem outcome.

But, if Voldemort was just told by Harry that the Elder Wand wouldn’t work against Harry because it belonged to Harry, and was a wand that would win any duel for its master, why would Voldemort willingly try and continue to use it? This is doubly so, since after he had cast the killing spell on Harry once it had only torn Voldemort’s soul from Harry’s body – wouldn’t that even imply that the Elder Wand would realistically refuse almost any attempted direct harm against its owner?

Also, wouldn’t a first refusal of the Elder Wand to kill it’s own master also imply an additional refusal even if Voldemort had won either of the Priori Incantatem matches (in which case, the worst that could happen in this line of thinking is, Voldemort has Harry’s wand since Harry’s spell is Expelliarmus)?

Answer 1

Two things here.

1. The happenings of the final of Deathly Hallows

The movie version shows the final battle similar to the "Priori Incantatem" shown during Goblet of Fire. However, in the book version, this is not the case.

In the book version, the final battle is pretty simple. Quoting:

Harry heard the high voice shriek as he too yelled with his best hope to the heavens, pointing Draco’s wand:
“Avada Kedavra!”
“Expelliarmus!”

The bang was like a cannon blast, and the golden flames that erupted between them, at the dead center of the circle they had been treading, marked the point where the spells collided.

Harry saw Voldemort’s green jet meet his own spell, saw the Elder Wand fly high, dark against the sunrise, spinning across the enchanted ceiling like the head of Nagini, spinning through the air toward the master it would not kill, who had come to take full possession of it at last.

And Harry, with the unerring skill of the Seeker, caught the wand in his free hand as Voldemort fell backward, arms splayed, the slit pupils of the scarlet eyes rolling upward.
Tom Riddle hit the floor with a mundane finality, his body feeble and shrunken, the white hands empty, the snakelike face vacant and unknowing.
Voldemort was dead, killed by his own rebounding curse, and Harry stood with two wands in his hand, staring down at his enemy’s shell.

(Emphasis mine)

2. Why did Voldemort go ahead even after what Harry said?

Simple. Pure unadulterated ego. He believed that owning the wand was what mattered, and did not believe Harry’s (Dumbledore’s) version.

He believed that owning the wand made him invincible, and was arrogant enough to further believe that a teenager had no chance of beating him, that too with a half cooked theory.