What could happen to them?
Loss of benefits. Full investigation, including spilling classified info. Prison, if Obama is feeling really PO’d.
They are taking a risk, big time.
I think any NDA they signed after the fact would be of dubious legality or enforceability. The worst that could happen to them is a legal hassle, that would be far more damaging politically to Obama than it could possibly be worth. That NDA won’t hunt.