Furthermore, if the plea agreement is void, it is STILL usable as evidence against him in trial. He signed a statement that the stated facts are true. He cannot avoid those admissions even with a voided plea agreement. It would not be legally operative, but it is still evidence and an admission against interest.
So in any follow-on trial, the plea agreement is evidence against him for the statements therein which he stated are facts.
The DoJ gamed him. He has no outs except worse alternatives. Any retrial and the plea agreement is evidence and his admission that the statements therein are true. Which results in another conviction. And this time without the benefits of an operative plea agreement to limit his sentence guidelines calculation and will also remove his credit for accepting guilt that was used for the downward departure.
The idiot thinks he was clever, but he just screwed himself.