2K Sports just announced on the Facebook page for NBA 2K12 that the game's demo will arrive on Tuesday, for both PS3 and Xbox 360, two weeks before its October 4 release.
The post offered no details about which teams would be featured but typically they involve last year's NBA Finals participants, which would be the Miami Heat and the world champion Dallas Mavericks.
The NBA lockout has effectively frozen all rosters as of June 30, meaning the teams will not be much different from what you played with at the end of the year in NBA 2K11. When the lockout ends, 2K Sports will publish a roster update that includes this year's rookies acquired in the NBA draft. They will not appear in the game until the labour issue is resolved and the league resumes play.