Compare emissions between France and Germany during dunkelflaute. Germany is frequently at the Polish levels of emissions and Poland is famous for huge emissions. Sunsetting would make sense if they could already generate enough green electricity even in bad conditions, which was not and is not the case. It was purely political decision - Germany wanted to be European hub for distributing gas from Russia (that's why tried to convince others than gas is somehow green energy).
Your question was how would the prices be without the nuclear shutdown, talking about emissions now is goalpost shifting. Speaking of politics and not making sense, Poland is still at these levels because they put road blocks into renewables deployment and spend their resources on nuclear plants. If those plans go well they will be at around 35% coal in 2040, which is more than Germany is now.
