A country in my world just bombed the entire continent. How much destruction should I expect?

Hi Worldbuilders, I know a lot of you here have experience worldbuilding for TTRPGs and that’s where this world is for. <br><br>So a lot of you know my world, but for the rest of you, the world is Earth but with magic and magical creatures. The over-arching storyline of this game is for one country to bomb the whole world an return it to darkness and magic. The premise is the country has hollowed out the continent and is using a magical core as a bomb to melt the surface of the continent. The continent is about the size of Australia. <br><br>Some of you have told me it would make the entire world uninhabitable, some have said the window of rain would be 100 miles around the blast site, and others have told me it would be as big as a SAC. <br><br>So we need to talk here about how big the destruction would be for me to set up this plot chain for the players and get them moving. We have another campaign coming up and then the players can start a new campaign and play as their own countries. <br><br>TL;DR: One Country is bombing a continent with a magical core. How much destruction should I expect?