Your scenario fails at the point that not declaring war on Russia if they invade a member state goes against the very basic agreements of the EU, so it would collapse the EU and all the member state economies.
Even AfD has only two choices if Russia invades Poland, sending the Bundeswehr or total economic collapse.
Failing a complete overhaul of the EU to be lesser, needing complete unanimity, the EU is a tight military alliance, tighter than NATO.
Your scenario fails at the point that not declaring war on Russia if they invade a member state goes against the very basic agreements of the EU, so it would collapse the EU and all the member state economies.
Even AfD has only two choices if Russia invades Poland, sending the Bundeswehr or total economic collapse.
Failing a complete overhaul of the EU to be lesser, needing complete unanimity, the EU is a tight military alliance, tighter than NATO.