By withdrawing Germany would not have lost the bulk of strength west of the Rhine which could have resulted in a much stronger defencive position which of course they should have prepared no later than early 1944. But of course the Allies would of had greater number as well.

The line up as it was then in March 1945 -

Germany
55 divisions (on paper) as we all know they were not all at full string.
Average infantry division 5,000 men

Allies
3 armies containing 29 divisions, more than a million and quarter men


I suspect in the what if situation the Allied study and planning in 1944 would have needed a bit of a rethink if the Germany army suddenly bolted back over the Rhine.

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Regards, Richard