Okay, so this theory actually came from my brother, which is odd because he doesn't comic book, like at all. I won't say that, he's a DC fan that straddles the line between casual and hardcore, he knows his stuff, but if you go too deep, you'll lose him.
Anyhow, I noted that the only color in the flashbacks of the decimated Avengers that you could see was red. Then he said that maybe it was because the Reality Stone is red and that they all were transported to a different reality when they blew into dust.
I was stunned, it's actually a pretty good guess! I mean, matter can't be created or destroyed, only transported. So that's completely plausible! Although poor Vision didn't get decimated, he just got the Mind Stone pulled right out of his head. So... he might be gone gone. Poor Vision.