Extracting your pound of flesh may be tricky. There's the blunt approach—refuse all help until he confesses on tape to everything he did to wrong you, from stealing you lab book to lying to Dean Green, to using your schematics to get here, to cavalierly usurping your future. Or, on second thought, perhaps you could have someone copy all Vance's emails, texts, notes, schematics, and other evidence on the laptop sitting inside the RV so that you'd have irrefutable proof.
Then again, maybe playing hardball isn't your style. You toy with simply saying you don't have any rope and so you'll need to go find some sturdy vines or some such. Then you can drive away and let him sweat bullets until you ride back to the rescue. Keep in mind, however, that saving Darien Vance is a risky proposition, no two ways about it, one that will be made harder the longer you delay as he sinks into the quagmire. It's time to make a decision.