I wouldn't be so sure about that. It may be impracticable, but it might still technically exist - the three remaining clubs certainly seem to think it does. The contracts were signed, and so clubs might still be liable for the withdrawal penalty that they agreed to, though no doubt the lawyers will be all over it.
Tbh, I've read nothing on this since it first came to light a couple of weeks ago, but I'm fairly sure that it's why those three are hanging on like grim death - they're so desperate for dosh they hope that they can somehow benefit from being the only ones remaining.