what was the plan if NATO itself had been attacked? Go ugly (nuclear) early?
We’ll if you mean throughout the Cold War until the fall of the Wall and the demise of the WP - yes.
Every exercise and plan involved a fighting retreat back to the Channel using the war stocks at hand and going nuclear around day 3.
It should be noted that the NATO nations still have the vast majority of their own war stocks, more than enough to finish off the remainder of the Russian armed forces. They just won’t give them to Ukraine in case they’re needed.
Though who else they might be needed against nobody quite seems able to explain.