re: Avengers Infinity War d23 trailer(filmed from a potato)

I doubt he destroys half the universe, though I could see some planets going down and possibly certain areas (Asgard, Knowhere, etc) of planets (as the trailer suggests) before Thanos even arrives on Earth. At the end of it all it's conceivable Dr. Strange could reverse at least some of the effects with the Eye of Agamotto.

I believe the idea is Infinity War is basically getting everyone together and Thanos actually acquiring all the stones. I expect he'll get the final one in the gauntlet towards the end and we could possibly see some of the heroes fall by then. Then Avengers 4 will be them all fighting him with the fully powered gauntlet so he's even more powerful.