re: How do behind the scenes trades work?

The CP3 to the Lakers was reportedly agreed to in principle before getting a veto from "ownership". So it probably is possible for the Asik deal to fall apart, but Houston has been trying to move him for quite a while now and no doubt had other options besides the Pelicans. It's unlikely the situation would change much over the next 2 weeks.

As for how the league handles enforcement of agreed to in principle deals, the league office does have to approve all transactions. I would imagine that if there was any documentation, like a chain of emails, the commissioner would not take kindly to a team reneging on an agreement and might force a deal through just like they occasionally veto some.