If Nvidia released a card with the exact same die, HBM, and everything, in place of its existing 980ti, it would sell 5x as many units and no one would call it a failure. Even if it was AMD who released the 980ti, Nvidia would still sell more.
Hold up, these reverse role posts always confuse me. And I don't want to lead into it with that asinine "so what you're saying" opener.
If the roles were reversed, you'd argue Nvidia would sell even MORE cards? I'm not sure how valid that is, but if the Fury X was faster, with more memory, used less power, and cost the exact same price as the 980 Ti I would not have a 980 Ti in my sig.
Now, I would think Nvidia would still out sell AMD (Fermi 480 vs Cypress 5870 anyone), but I doubt Nvidia would sell 5X more units than what they did now.