They couldn’t. But they could have told him to report and if he didn’t play, he wouldn’t have been paid. Not sure how many seasons he would be willing to sit out under that threat. Maybe all of them, but Houston could have controlled it a bit. That being said, they clearly just didn’t care. They know they are going to be horrendous for a few years. Having 2+ firsts in each of the next 3 drafts will help.