If he got it just verbally then I can't see him having a case, they can claim they didn't say it and that will be hard to prove, it might still work but that's very thin ice.

If he got it written into the contract then it is clear that he does not intend to pursue it.

If it was written into the contract and he pursues it then he will need to show that he has suffered because the contract was not executed and I fail to see how he could make that case and do so with enough teeth that it would matter to FB enough to reverse course.