Well, not to confuse the issue here, but a good grain crusher will strip off and leave the husk (hull) more or less in one piece, and shatter the body of the grain into maybe 6 pieces. And in a pound of grain milling, I would expect a very small handfull of "flour", or fines.
BIAB or traditional lauter-tun can both leave some fines in the wort, but they will settle out and not be a factor long term, in my opinion. So to answer your question I think much of the flour can escape the bag. But virtually all, 100%, of the grain "dust" will settle out in your fermenter if you give it some time.