The hypothetical is so “out there” that it is tough to answer.
Everything depends on context.
What are the circumstances that lead to the attack? The German nationalism that led to two world wars was based on two factors no longer relevant-The unification of a confederation into a greater Germany, and the re establishment of liberal values instead of Prussian authoritarianism.
I don’t believe Alsace and Lorraine are still an issue between Germany and France.
Germany no longer owes impossible war reparations.
In my opinion;
If Germany harbors some post World War II frustrations that could lead to war, it has more to do with Poland’s borders and Konigsberg, and not France. If anything about the hypothetical might emerge, it would probably be a movement to the East, not the West.
Plus, to be honest, it is unlikely that anybody is going to wage the kind of war where armored divisions sweep across broad chunks of territory. Nobody has that kind of money these days, and most of the liberal democracies do not have an electorate that would stand for it unless there was a perceived security threat. The real threats now are cyber attacks on markets and defense systems.
Finally, if Germany decided to become aggressive, the NATO allies would convene and discuss what the ramifications would be if it became a problem. The answer to your question would emerge before it happened.