I think the only thing keeping Parker out of the top 3 is if he choose to go to the draft, but doing his mission first. Some of the bottom teams wouldn't want to wait a couple years for a player. Especially if he's away from high competition for two years.
Now he can do part time from what I understand, but Im not sure how it works. If he can spend his summers doing them until he fulfills is agreement, that could also change some things.
But one bad game doesn't really hurt his stock too much. It may change the 1,2,3 spots depending on how well Wiggins does, if Embiid comes back. MAYBE if Randle has a good show, he gets bumped up, but unlikely, but who would have thought that Bennett would have gone #1.
If anything from a bad performance I could see Parker stay a year and work on his game. I think the poor showing will also help Silver and wanting to keep players from entering until they are 20. Parker clearly looked over whelmed by the big game.