Well it's hard to see the precisely consequences, Sweden wouldn't in the worst case lose much of it army, and even in the good case, it would suffer heavy losses. Denmark could quite well force a white peace or even a return of the 1645 borders if most of the army has gone through the ice. If Charles die, we will likely see a faster end to the fightings in Poland too. Frederik III of Denmark may still be able to force absolutism through. But I don't think we will see as extreme version as OTL, likely Frederik has to use the French/Brandenburgian model where the estates still exist in theory, and the nobles get freedom from taxation for not calling them. Demographic Denmark are a lot better off, Zealand was always the demographic centre of Denmark, and was used to repopulated Jutland and Scania when a army had gone through there. The invasion in OTL hit the entire Denmark hard with quite enourmous losses, a third of the population died over a periode of three years as people can imagine this was a major national trauma, much worse than 1814 or 1864 wich was incredible traumatic in their own rigth. Political the war changed Denmark-Norway from a noble republic to de facto the Kingdom of Copenhagen and its possesions. While we will see something of the same, it will happen to much lesser extent, with a stronger nobility.