Actually the NBA will be declining on the heels of the NFL.
I agree that it will probably decline, just not as fast. Blacks will still watch it.
I believe right now the NBA is more popular outside the US than inside. It is very, very popular in China. I have seen Chinese newscasts where they cover the scores just like a local evening news broadcast here does.
If the NBA viewership collapses inside the US, it would still not bankrupt the league, because of foreign ratings. The teams would just migrate to foreign cities outside the US.
Actually the saving grace of the NBA may be the Euro players, who at least reduce the thugball aspects of the League.