THE GAMER NEXT DOOR

Answer: It's a healthy, plant-based smoothie. Tony is drinking them in several MCU films.

Answer: He mentioned in an interview that a lot of characters were going to die. Recently on the Graham Norton Show he revealed that he had his phone on and was live streaming the premiere of the movie towards all his followers, by accident. Only for 10 minutes or something and only audio.

lionhead

Answer: He does it for three reasons: 1) They served their purpose. His goal was to wipe out half of the universe and he succeeded. 2) To avoid the temptation to use them ("they served no purpose, other than temptation.") and 3) So that the destruction (his "work") will always be, that is to say it can't be undone.

Bishop73

Answer: He said "they had served their purpose" So he is arrogant enough to believe that once the stones had done what he wanted them to do he destroyed them as they were no longer useful. But its also possible he didn't want anyone to reverse what he did.

lionhead

Answer: He was probably contemplating what to do with himself and the stones now he had fulfilled his purpose.

lionhead

Answer: Being regular humans without powers or highly advanced technology, they may not have been able to fight properly against Thanos' forces.

LorgSkyegon

Answer: Spoilers! Given what we see in Spider-Man: Far From Home it may be that they were offworld doing other vital work.

Answer: Since any reason given would be speculation, the easiest explanation is that they had something else to do in this, the one and only future where the Avengers won against Thanos.

Answer: Cassie was born in July 2007. So during the future scenes, she is either 16 or 17.

LorgSkyegon

Answer: No - as stated in the film, timelines/realities are independent from each other. Thanos/Nebula coming to "our" timeline means a new timeline is created where they don't exist any more, but we don't follow that one. "Our" Nebula isn't affected by the actions of the "alternate", because "our" Nebula's history is unchanged.