Would it be defensively easier to hold with better logisitics? Further, would the Germans be more apt to withdraw from the middle of nowhere?
Yes and possibly yes. Although given Hitler's frequently irrational contempt towards giving up land, regardless of it's value, I qualified the latter statement. I could easily imagine him issuing a no withdrawal order with the justification that holding the Don-line would keep the Soviets away from the Donbass or some such nonsense. It should be observed, though, that even if he issues a "hold at all costs" order, there were points later in the war where German generals disobeyed those kinds of orders and didn't suffer for it.
Well, the Germans will be worn by fighting so their numbers will be depleted, though not decimated. Nonetheless, the Russians will qualitatively out number the Germans by a crap ton.
Agreed.
The Germans will have to withdraw, though this might make the "backhand blow" more devestating as they will be in a beter position to do it and will have not lost half their heavy equipment.
The flipside is that the Soviets are also in a better position to receive the backhand blow. IOTL, it was launched against a force which had strung itself out and pushed far beyond their railheads in the wholesale rush for the D'niepr. ITTL, the Soviet winter offensive will probably be more akin to Operation Suvorov/Orel then either Operation Star/3rd Kharkov or Operation Rumyanstev/4th Kharkov, albeit somewhat more favorable to the Germans. We're looking at the Soviets steadily pushing the Germans back from one defense line to another here instead of a more straightforward breakthrough-exploitation attempt.
On the whole, this is a POD has the odd effect of being better for
both sides: they will still take heavy losses, but the Soviets avoid the decimating losses in both military and economic terms of summer 1942 and the Germans avoid the over-extension and decimating military losses at Stalingrad during the autumn. The war will still tip in the Soviets favor, but it will be more of a steady slide rather then the abrupt reversal of IOTL.
Well, assuming the Germans aren't still overstretched enough that they have to give a notable portion of the line over to one of their Axis minor allies. If they do, then you can bet the Soviets will hone in on that weakpoint like a magnet.
It would be far too little to do anything, right? WOuldn't the army get decimated against entrenched defenders?
In all probability it gets cancelled by a Soviet offensive designed to pre-empt and deflect it, like it was IOTL.
So, do they call it off or is it in effect a big Russian victory?
Likely call it off.