To sum up, if Charles the Bold have a posthumous son with Margaret of York, it means that Mary of Burgundy doesn't inherit. France still get the Duchy, because let's face it, Louis XI would find a way to ensure that the Burgundian heartland remains under direct French control. As for the Burgundian territories not an appange of France however, that son still inherits it.
No Burgundian succession means Austria doesn't get the wealth acquired through the Flemish trading cities. Who knows what other butterflies may occur out of this?