I don’t believe you can put an arbitrary financial penalty on something like that. Closest you could get is “no recording of meetings” in an NDA. However, if the allegation is breaking of the law, which this seems like since they are attempting to fire for cause instead of it being a layoff, you can’t cover illegal activity with an NDA. Meaning this would still be releasable.

Though I’m not a lawyer, so don’t take my random rambling as legal advice.