Interesting, how do you judge a "brand in decline"??
Ducati as a brand can no longer command the same brand premium they once di but thats because of market forces and the economy. Their racing profile is lower than the glory days of Foggy/916 mid nineties but given that Vale dominates the mainstream press its hard to alter that.
As brand its got all the things you look for brand loyalty, solid customer base, aspiration-al and the products have innovative design and are unique.
Its recent co-branding products with other high image brands - Oakley, Burton, Briel suggest that the corporate marketing world still sees value in Ducati.
They haven't started sub licensing to other companies so still retain complete control of the IPR.
My opinion, for what its worth and using the above criteria is that its not in decline