Well, the issue is, while they were waiting, Deng was signed. Ariza was signed. Hayward was signed. Bosh was signed. Lebron and Melo were signed. Wade was essentially locked up.
That all happened before Dallas had a shot to do anything because of that Parsons offer sheet. They made their bed with that offer. Even if HOU matched, all that is left is someone like Lance Stephenson.
Even guys like Marvin Williams, Lin (who was available to absorb into cap space + would have netted a pick), Isaiah Thomas are all gone.