Dude was HILARIOUS. When he was sitting in the chair and they were asking him about the Aether. I instantly thought of Weekend at Bernie's the way he was sitting lifeless. Is he sleep? No he is definitely dead.
No but at the end of Infinity War it was. Dude didn't say he was leaving a legacy something that out lives you, he said destiny fulfilled.
He changed his goal because even after performing the snap the survivors remember the time before and will fight to return to those days. So Thanos decided I am going to erase all life in the universe and rebuild it how he saw fit.