Well he was created by an abusive drunk as a means of wishfulfilment... so really it would depend on who was writing.
Like, if it was Fletcher Hanks writing Korra would go all Avatar State, but prior to an epic battle Stardust would just raise an eyebrow, and her arms and legs would sprout wings and fly away or something. If it was the people in the show writing, then they would have an epic battle that would presumably end with Korra depowering/killing him.
Funny thing, the SpongeBob comic did a homage/parody of Stardust. http://comicsalliance.com/paul-karasik-r-sikoryak-fletcher-hanks-stardust-spongebob-squarepants-annual/