Could Germany create a defensive line behind the Dnieper and Daugava rivers shortly after the battle of Kursk
How effective would such a defensive line be
how long could it hold the Soviets off
How would this impact world war 2
Which battle of Kursk? The German offensive or the Soviet ones? Plus we'd have to wave Hitler's entire standfast mentality and demands to hold the Donbas.
Assuming you mean Zitadel there is the problem of the Orel offensive by the Soviets being dealt with and the need to retreat in various phased withdrawals, plus the actual attempt to construct the
Panther Line, which never really got built. The Daugava is too far back, the Panther Line, which ran from Narva in Estonia south was the only realistic line of retreat from 1943 positions. If that is the plan there is probably a series of phased withdrawals throughout July and August, which probably frustrates Soviet plans to attack in Ukraine and Belarus, but gives them a lot of terrain without a fight, though probably territory that has been scorched earthed and denuded of military age males. If they could pull that off with an intact army they stood a serious chance of holding strong for a good long while that would be very expensive for the Soviets to break, while giving time build the next defensive line. If they are meticulous in their scorched earth and evacuating of military age men, they could well bleed out the Soviets, as the Soviets did recruit some 4 million men from territories liberated in Summer 1943-1945. With more time and effort to recruit from the Baltic states they might have a tad more manpower themselves in 1944-45.