TL: DR : Han var säker på att han var 100% garanterad att döda Harry. Han hade därför ingen anledning att fly. Han visste inte att alla andra Horcruxes förstördes innan Harry berättade för honom.

Detta utarbetas i böckerna (observera att Nagini dödades långt före den sista kampen - utanför slottet)

“Potter doesn’t mean that,” he said, his red eyes wide. “That isn’t how he works, is it? Who are you going to use as a shield today, Potter?”

"Nobody,” said Harry simply. “There are no more Horcruxes. It’s just you and me. Neither can live while the other survives, and one of us is about to leave for good. . . .”

“One of us?” jeered Voldemort, and his whole body was taunt and his red eyes stared, a snake that was about to strike. “You think it will be you, do you, the boy who has survived by accident, and because Dumbledore was pulling the strings?”

(DH, Ch. 36, "The Flaw in the Plan")

Och längre ner:

“Is it love again?” said Voldemort, his snake’s face jeering. “Dumbledore’s favorite solution, love, which he claimed conquered death, though love did not stop him falling from the tower and breaking like an old waxwork? Love, which did not prevent me stamping out your Mudblood mother like a cockroach, Potter— and nobody seems to love you enough to run forward this time and take my curse. So what will stop you from dying now when I strike?”

“Just one thing,” said Harry, and still they circled each other, wrapped in each other, held apart by nothing but the last secret.

“If it is not love that will save you this time,” said Voldemort, “you must believe that you have magic that I do not, or else a weapon more powerful than mine?”

“I believe both,” said Harry, and he saw shock flit across the snakelike face, though it was instantly dispelled; Voldemort began to laugh, and the sound was more frightening than his screams; humorless and insane, it echoed around the silent Hall.

“You think you know more magic than I do?” he said. “Than I, than Lord Voldemort, who has performed magic that Dumbledore himself never dreamed of?”

(DH, Ch 36.)

Eftersom han trodde att han var äldste Wands mästare

Voldemort arbetade under det intryck att han var den äldste trollens herre. Den äldste staven är den mest kraftfulla trollet av allt, så det var helt enkelt Voldemort som trodde att han var garanterad seger över Harry. Det var förmodligen varför han inte försökte fly - när Harry Potter dödades kunde han senare göra mer horcruxes för sig själv. Han ställdes inför chansen att döda Harry, en möjlighet som inte kan presentera sig i framtiden. Med tanke på Voldemorts hat mot Harry, och trodde att han hade mästare i den äldste Wand såg han inte något behov av att fly.