"People" always used to say that if you got into Harvard it was impossible to flunk out but I never thought to look into that statement since it has never had any relevance to me.
I'm speaking from personal experience.
I made a minor attempt to drop out of law school, as in refused to do a requirement of the school (by showing up and informing them that I was not going to participate) and then explain that the reason I didn't do it was because I was thinking about dropping out (which was true). Duke talked me out of it and made special accommodations so that I could complete the requirement.