Comments by "Sar Jim" (@sarjim4381) on "Battlegroup Böhm - The Furthest German Advance West, Ardennes 1944" video.

Even if they had sufficient fuel, the Germans could only advance as long as bad weather kept allied air power grounded. Once the skies cleared, most of the German armored vehicles were destroyed in concentrated air attacks. What the Battle of the Bulge proved was no modern armored offensive could succeed without air superiority. This proved again - twice - in the battles for Kuwait and, later, Iraq.
41
A static defense along the Rhine would have been useless. There weren't enough prepared positions or manpower to hold the entire length of the River. The allies would have used a combination of air strikes and superior troop and armored strength to destroy weaknesses in the line and pour across the river. Once they had enough strength across the river they could turn and destroy the Germans left isolated along the river since they had no escape. Once the D-Day landings succeeded, Germany was doomed. A more interesting question is what would have happened if Hitler had not attacked the Soviet Union? With a much greater ability to resist attacks in the west and the Soviet Union not part of the Allies, the outcome would have been much different.
17