ALERT MAJOR SPOILERS. okay so marvel has a pretty bad record of spoiling big moments in their trailers. They spoiled the end of the avengers when you think that iron man is going to die but the hulk saves him ( which was in the trailer) after that they spoiled that nick fury would die in captain america the winter soldier in the 2nd trailer for the movie. Even though nick fury didn't really die it was still a pretty big spoiler.
But let me get to the point of how I knew how quicksilver was going to die in avengers 2. in the first teaser for the movie their was a scene that showed the scarlet witch SCREAMING and then it was later announced that an avenger would be dying in the sequel so I went back and watched the teaser for any signs of who would be dying. I'm pretty sure most people thought that captain america would be dying because of the broken shield in the trailer but they had already announced civil war so you can cut him, iron man, black widow, and hawkeye because they were pretty much confirmed for civil war. And don't forget about thor who is getting his third movie so you can scratch him off two so the only possible characters to die in the sequel would be one of the maximoff twins and scarlet witch basically spoiled WITCH avenger would die . you see what i did their with the witch thing ?