What an ending that would be: Harry uses the Self-Indication Assumption to conclude that he is most probably a character in a Muggle story about magic, then manages to 'blackmail' the author into granting him godhood in order to stop Harry from committing suicide in a literarily unsatisfying fashion, since the author would prefer the former as an ending over the latter. Someone would object that Harry doesn't have agency? But he does, if the author takes the character seriously and continues with a high-fidelity in-character continuation. If Harry found out he's likely a character in a novel, he'd be right, and there's no reason he shouldn't use that to his advantage.

Talk about writing yourself into a corner! :)

EDIT:

"It's not going to work!" Harry was shouting at the top of his lungs, his wand pointed at his own temple. He gripped it so tightly his knuckles were white. "You wrote me this way, you know there's no going back from this point, you knew I'd find out eventually."

Ominous clouds were forming, a harsh wind picking up, making Harry shiver from where he stood in the Hogwarts central yard. Students stood aghast, staring at the screaming boy pointing the wand at himself.

"And you can stop with the weather charade, if I do this -- and I will, your book will be ruined, those little touches of drama aren't going to fool anyone!"

"Harry." The cold voice of the Defense Professor carried over the noise of the wind effortlessly, yet seemed spoken with little effort. "I have new ... " Quirrell pointedly glanced at the students present. "... information regarding your quest. I don't know what you are trying to achieve with this, but it may be best we go inside and ..."

Harry scoffed -- actually scoffed at his mysterious ancient wizard. "Silence, Mr. Intriguing-Plot-Point! I shouldn't even be talking to you, not any more! I won't be distracted, this ends now, one way or another. Which ending will you be writing, Mr. Not-Quite-Omniscient Author? None of your characters will make me back out of doing what's right! If you write this novel, I will make sure it's an utopia, or I'll ruin it!"

"Harry!" A wide-eyed Dumbledore appeared as if out of nowhere next to Quirrell. "Harry, my dear boy! Stop this madness! This is not what the hero is supposed to -" "You know, Headmaster, I don't blame you for your failures, for not seeing the obvious. That, too was part of the plot. You see," Harry's voice was dripping with condescension. "You weren't supposed to be endowed with enough agency, or to be taken seriously enough, to actually come to the right conclusion, and to cut your own strings. You remain the puppet ... with all due respect."

"Harry Potter. You and I have unfinished business!" Draco Malfoy, his father's spitting image, strut upon the courtyard. Harry didn't even look at him. Draco stared incredulously as Harry looked up at the sky, and continued to shout against the wind. "That must be some sort of movie allusion. Getting desperate, Mr. Author, aren't we? You won't salvage this ending, no matter how hard you contrive to. This show is over, no more diversions. It's time to end this!"

The wind stopped abruptly. Harry turned around, to find the courtyard empty. Only a certain twitch of his eyes betrayed that he had come to a decision, that he was preparing to act. The wand pressed ever harder against his temple, he opened his mouth to speak the final words. Had he overreached with his precommitment? I can only go forward, if I stop, I'm lost.

"Harry, oh Harry." A soft female voice said from behind him.

He knew that voice.