Well first off, when does the point of divergence begin? If it begins after Zitadelle, then no work has been done on any rear defensive line. Even if
Heeresgruppe Nord began a withdrawal from Leningrad immediately, this wouldn't free up enough forces for
Heeresgruppe Süd to hold the historical Wotan Line. Granted, Von Manstein might've had a chance of snuffing out Soviet bridgeheads on the Dnieper, but he needed more forces. These forces could've only been acquired by abandoning the southernmost portion of the Wotan Line. This means no Donbass coal, no delusions of grandeur about a second invasion of the Caucasus, and the acceptance that the Soviets will have "an unsinkable aircraft carrier" from which to bomb the Romanian oil fields.
Keeping in mind, 17.Armee was still holding the Kuban bridgehead until October 1943. Unless they were going to evacuate Crimea by sea as they did OTL, Von Kleist must hold the area between the Dneiper Bend at Zaporozhe and Melitopol at the Sea of Azov, while 17.Armee retreats across the Kerch Straits and then across the Isthmus of Perekop. If this retrograde movement isn't started early enough, German forces will be stretched too thin. This means, as OTL, the Dnieper Line will be compromised, a massive gap known as the
Wehrmachtsloch will form between Von Kluge's and Von Manstein's army groups, and Von Kleist's army group will be pushed toward the Southern Bug.
Meanwhile, a withdrawal to the Dvina is a complete non-starter for Hitler. Even after the start of Bagration, the combined efforts of Göring, Schörner, Model, Zeitzler, and Frießner could not get him to budge.
Here are the following reasons:
- Loss of Estonian oil shale.
- Loss of Swedish steel.
- Loss of Finnish nickel; likely loss of Finnish alliance as a whole (if Dietl's death is butterflied away, maybe Hitler feels better about the situation).
- Loss of U-boat bases (this was Dönitz's main argument).
- Loss of minefield blockade in the Gulf of Finland; Soviet submarines break out into the Baltic Sea.
However, Hitler was willing to accept a withdrawal to the Panther Line, from Narva, Lakes Peipus & Pskov, down the Velikaya River. Yet, even permission for this couldn't take place until January 1944. Meanwhile,
Heeresgruppe Mitte lost its entire section of the Wotan Line and only held onto a small portion of the Dneiper between Orsha and Mogilev.
In short, the Dvina was absolutely unacceptable for political-economic reasons, and the Dnieper was likely already doomed unless radical policy changes are introduced in spring 1943.
