There should be a number of factors that come into consideration IMO.

You should look a their history of the past 20 to 30 years or from the time they entered the league if they're a recent expansion team.

1) Do they have a tradition of winning? Have they, in the above period, shown some sustained success?

2) What are their attendance figures like? Do they have a strong season ticket base?

3) Are they in a large media market or small media market? A larger media market should get more consideration for sticking around.

If the above factors do not favor your team, you should be contracted. I think the following teams are prime candidates based on the above.

Bucks
Raptors
Hornets
Bobcats
Timberwolves
Kings (Before they were moved.)

The Pistons do not fall into that category. The last four years have been bad, but they had 5 straight runs to the ECF, two Finals, and one chip. And that's just the past 10 years. Prior to that was the Bad Boys with two chips and battles with the Lakers, Celtics and Bulls. Not to mention they have led the league in attendance many times over.

I'm all for contraction. Getting rid of 5 or 6 teams would result in a much, much stronger NBA. The talent pool would not be as diluted as it is now and the league would be much more competitive.