Actually, Sushi is not made from raw tuna, or any other fish, by definition.
Sushi is simply small portions of cooked sticky rice. It is sometimes served with raw or cooked fish. More frequently, however, you will find it rolled with pickled vegetables, wasabi, and a seaweed wrap.
Sashimi is raw fish. You will likely find sashimi to be served cold, sliced thinly into slabs, with shredded vegetables, pickled ginger (yum).
So, while sushi may be served with raw fish, the non-existence of raw fish does not in anyway invalidate the existence of sushi. Sashimi, on the other hand, cannot exist without raw fish.
A wonderful fresh Ahi Tuna does make a delectable and tender sashimi. A good one, deep red in color - yet eerily translucent - will melt in your mouth. You will never forget they sheer gustatory and olfactory ecstasy you will experience. Never.
I sure hope the rumor is true. I love fresh sushi and sashimi!