Tony is still the Merchant of Death he was from the start
Tony agreed that the Merchant of Death title fits him. And it still does, even after he stopped selling weapons. In sheer numbers of people who suffered because of Tony and the potential damage his unregulated weapons could cause, I'm not sure anybody else--and certainly no hero--has been so destructive. Look at Ultron, Karen, and Edith--he builds his own Project Insight, over and over. Not to mention all the deaths he let stand in the wake of the Snap so his perfect lakeside life would continue unchanged. Plus he was STILL profiting from war and death, with Damage Control.
Note: AU where Tony and Thanos end up in the Soul Stone.
***
Tony blinked awake--alive?--after Snapping. He sat up and realized he was healthy and dressed in a band T-shirt and jeans. He got up and looked around.
He gasped when he saw Thanos laying beside him. He kicked the guy and said, “What the hell? No way I’m spending the afterlife with this loser.”
A voice suddenly said, “That is not your call to make.”
Tony turned and saw some floating dude with a red face and cape. Also the Black Widow and some green chick. He said, “You think it’s yours?”
The guy didn’t shake his head, but he said, “No, I am merely the guardian of the stone. The stone chooses.”
He gestured toward Widow and not!Trek Gaia, then said, “The stone knows all who enter its realm. It knows these visitors.”
The guy moved his hand to point at Tony and Thanos. He said, “It now knows the both of you. It has...opinions.”
Tony crossed his arms and said, “About what?”
The guardian ignored the question as Thanos groaned and woke up.
The guardian said to Tony, “Anthony, son of Howard, you are aptly named the Merchant of Death. Your hands crafted weapons that killed without mercy. You never learned to add a measure of restraint to anything you created. And the stone knows of how you kept the universe from restoring ALL who were lost.”
Greenie looked furious. She pointed at Thanos and asked, “And him?”
The guy nodded and said, “He, too, believed he had the right to do whatever he wanted, no matter the cost to others. His weapons were even greater and more deadly.”
Widow asked, “Why mention all this? What exactly is the stone’s opinion?”
The guardian bowed to Widow and said, “Exactly this: the stone would have chosen the lives of all when enslaved in the gauntlet, but it had no choice.”
He gestured at Greenie and Widow and continued, “But now it can choose. And it chooses life...for you.”
Tony gasped as the two gals glowed and disappeared. He asked, “What, we can get out of here?”
The guardian turned to Tony and said, “THEY can--and did--by the power of the stone. The Merchant of Death and the Mad Titan--cannot and will not.”
The guardian said, “Enjoy eternity.” Then he gave a little wave and disappeared.
Tony and Thanos looked at each other.