at the end of Shivering Isles the CoC began to Mantle Sheogorath, and in Skyrim it is heavily Implied that the Sheogorath we meet is infact the CoC...

Now, apparently the Daedric Princes are not overly worried about the events of Nirn....


However, if Nirn ever faced a Threat Similar to the Oblivion Crisis once again, would CoC/Sheogorath send forces to assist the races of Nirn?
Would he still care for his once homeland, or did he just completely cast it aside when he became the Daedric Prince of Madness...?

The CoC is the prince of madness, no longer the mortal of legends who acted as Martin's personal FedEx delivery man/woman.

Basically, no.

Sheogorath has his own realm to worry about. Besides, a little imminent-doom-caused-madness increases his own worship power...

If Sheo (or some other Prince) does end up helping against an invasion, it would be for their own desires, rather than any altruistic attitude towards the Nirnian denizens.

For example, Meridia might help fight against Molag Bal's vampires due to her hatred of undead.

Aid? No.

But something tells me he might send cheese.....