As long as they continue to dominate the key advertising demo (males 18-49), the money will always be there. Game 3 beat everything except the NFL (which it's never had to compete against before), had a 2:1 advantage over its closest competitor in Game 1, and enjoyed a 4:1 advantage over its closest competitor in Games 3 and 4. If the NBA can continue to average a 3:1 advantage in the key demo over everything else it goes head-to-head with, that TV money ain't going anywhere.
The disclaimer is, if there isn't a way to advertise on the different mediums and the current means of advertising is still the most effective, then you are probably right, the money will stay. But I wouldn't bet on advertisers not being able to come up with a way to get into any game.