i could see Alexander living a full life, and perhaps hitting multiple defeats somewhere later in life. Judging by what i've read of him, he would send explorers out. Especially after reaching the pacific ocean. If you look at the differences in cartography pre and post Alex, there is a noticeable shift in knowledge of the world. If he did conquer his way to Southeast Asia, im positive he would say "well theres two oceans on either side of us, lets see if they connect.
And at that point, the Native Americans have an entirely different fate.