No Stark, Sherlock
The minute Iron Man flew the nuke through the portal into outer space and towards the mother ship, Loki knew it was over. Using the last of the magic he could gather, he used it to transfer Tony back to the 1800s in another universe. Loki might have lost the fight, but the Avengers lost Tony Stark.
The last thing the avengers saw was Iron Man carrying the nuke through the portal, before it shut and all the invaders fell over dead all at once. They stood there staring at the sky for what felt like hours, the silence surrounding them heavy while they waited in vain hopefulness for any sign, that Tony had somehow made it back, that he had got through the portal at the last second, and was just hiding behind a building, about to pop out and they would all get Shawarma. After a while, they set off with heavy hearts, and despite winning the battle, they might as well have lost. Tony Stark was proclaimed dead to the public the next day, as chance of survival was slim to none. Little did they know that in an alternate universe, 200 years in the past, Tony was starting a new day as Sherlock Holmes.