Wrong on all accounts.
First of all; As said by Odin, the Asgardians ARE mortal, they only live longer.
And according to Superman; All Star, the radiation of our yellow sun has strengthned Superman's cells so much, it would be impossible for each of them to be fully destroyed. So, c ombined with the accelerated regeneration of his super-powered cells, Superman litterally can't die. (Keep that in mind whenever the next Goku vs Superman discussion comes up)
Second, the notion of Superman being weak againts magic, is also misunderstood, eventhough Thor uses magic
It depends on how it will be used, if the magic is used to make weapons, or kryptonite base weapons.
In this case, Thor's magic comes from his hamer, Mjolnir.
But the magic's effect on Superman would be cancled out, because Mjolnir is made from the matter of a star.
Stars, like our yellow sun, are what give Superman his powers.
By that logic, despite the awesome film by Bat in the Sun, a single hit from Mjolnir would strengthen Superman.
Thor would be commiting suicid
but what if it was made inside a red star(i think one version even says it was made inside a dying star i think. dying stars are usually red giants) red stars have a radiation which i think kinda weakens or corrupts supermans powers if im not mistaken...
