They won't contract. Maybe a couple of unnamed owners are willing to throw it out there to scare the players that they could lose 30 jobs with two contracted teams, but it won't happen. Maybe it's also to scare the owners of a few of the major market owners for more revenue sharing. But it's not a real idea.
Contraction means that the next TV deal the NBA gets will be worse, because it means ESPN, Turner, or some other network will question the NBA's viability if they are the first major US sport to eliminate a team in the national TV era. That means less money for all the owners.
Contraction means that the remaining owners will have to pay the owners of the contracted teams hundreds of millions in buyouts. The Golden State Warriors sold for $450 million last year. I'm certain there's someone out there willing to buy New Orleans and Charlotte for $150 million (a third of $450 million) as a very conservative estimate, which means that the other owners desiring to contract those teams would have to pay more than another buyer on the open market would. No way they're doing that.
Contraction means that the value of all the other teams falls, for reasons beyond the money lost due to my first two reasons above. If the league looks like it might be losing its viability, or that further teams might be contracted, owning a team is now a riskier investment for future potential buyers of NBA teams, and therefore they will want to pay less for that investment. The value of the Warriors tripled in 15 years. Contraction kills that growth. Again, no way is there going to be contraction.