Well, no one seems... Upset or unsettled, nor gives any hints that the Decimation (The confirmed official name of the dusting.) ever happened. (This movie is suppose to start directly (Like, minutes.) after Avengers: Endgame ends.) I'm thinking the Avengers completely reverse it. (With dire consequences.)
And notice, Harold "Happy" Hogan says "You're all alone," like, why aren't the Avengers coming to help the Spiderling out? I mean, London is being attack by three (Possibly four.) giant elemental monsters, I'd say that'd usually be of the Avengers' interest. Of course, one could argue that the Avengers weren't sent out by the government (They can't do anything unless the government clears them because of the Sokovia Accords as of Captain America: Civil War.) but you'd think that they'd help anyway.
Now, at the end of the trailer, a boy says that Mysterio is like "Iron Man and Thor rolled into one.", he mentions them with no remorse, as though they're not dead, if the world was mourning a recent loss of the two superheroes that had saved them so many times, they would probably not call them out by name without batting a lash. But that doesn't mean they aren't dead. (Probably just Iron Man would be dead.) What if due to meddling with the timeline, they mess up and something happens and they die in the battle of New York? Like Tony doesn't come back through the wormhole?
and making me no longer want to see it. I am going to imagine that Endgame was successful at the cost of Captain America. (Cause Chris Evans won't do anymore movies) So that leaves all the other Avengers alive. They need info on Thanos. So Antman and Iron Man go back to The Battle of New York to extract info from Loki. Loki is (expectedly) not helpful, but shows up while they are gone and ticks everybody off Antman and Iron Man return and Loki is grilled. Thanos is discovered and decapitated. Everyone is happy. 
