I agree. Other than something in the 1930s, the most likely scenario I can see is if Hitler is assassinated (or otherwise dies) and there's a struggle for power thereafter. I could imagine one group trying to sue for peace while another wants to continue the war. Again, the timing is huge.
I still have a hard time seeing a true civil war. Perhaps the best option for that is if Hitler dies and then hardcore Nazis with similar mindset seize control in Germany. Then some senior military leaders that are farther afield (Africa, Italy, Russia, France) bring some of their forces back home to try to seize control -- kind of like the various Roman Legions that tried to seize Rome.
You're right that, in any case, if it gets beyond a swift coup (on whatever side), Germany likely ends the war soon, one way or another.
Here's one idea:
- Hitler dies in mid 1942
- Himmler or Goering seize control to continue the Nazi plan
- Paulus, in coordination with other German leaders on the Eastern Front, secretly negotiates with the Russians and reaches agreement that they'll pull back to the original pre-Barbossa lines (with a buffer zone) if the Russians will agree to peace.
- To this point, things have been going very poorly for the Russians, and little allied assistance is on the horizon, so Stalin agrees.
- USSR agrees to separate peace with Germany
- Paulus pulls back his forces and has some establish a strong defensive front
- The new Nazi regime brands Paulus and those that follow him traitors
- Nazi regime asks all generals afield to return to Germany for consultations (verification of loyalty). Most, including Rommel, make no response to the order, but Kesselring returns and stays to assit
- Paulus quickly brings a few divisions to Germany to seize control
- Some units in Germany refuse to fight Paulus, but others do
- Nazis summon some forces from Germany and Italy to fight the traitors. Some return.
- Paulus defeats those units that fight him and seizes control
- Italy recognizes Paulus
- Rommel refuses to state loyalty and asks Paulus' intent
- Paulus begins negotiations with the Allies and requests Rommel to re-deploy his army to Sicily / Italy
- Rommel, receiving even fewer supplies, orders the Afrika Korps to withdraw and they do so with very little opposition
- Italians continue fighting (badly) in Africa
- UK, with American assent, agrees to peace in Europe by 11 Nov 42. In Western Europe borders return largely to pre-war
- Italy is defeated in Africa and agrees to peace, abandoning all pre-war gains
- US and UK largely concentrate on attacking Japan, but build up forces in newly freed France to defend in case Germany attacks again
- Europe settles into a very tense peace. France and low countries are freed, but Germany maintains gains in the East and Balkans. Russia maintains pre-Barbossa gains and continue modernization
- Japan is defeated in mid 1944, before A-bomb is used.
I think Hitler would have to be gone for any civil war to arise. .. Any time in between a civil war would probably end in a Nazi victory, as they were better organized and had more firepower and support. After the war started the biggest effect of a civil war would be hastening the collapse of Nazi Germany.