IANAL but I think, if you have legally hard evidence of the threat you can bring that up at the initial hearing of any lawsuit filed against you and/or your company. This should increase the chance the lawsuit will not be accepted in the first place. I guess few judges like the idea of being used as a weapon in a personal quarrel between company CEOs.
It might also qualify for a counter lawsuit for coercion (I'm not a native speaker either, maybe the correct term is "duress"). That's especially, if there was an "if" attached to "I can bury you in lawsuits". It can easily be a case of attempted extortion as soon as any condition was implied.
However "legally hard evidence" is not easily obtained with people too clever to
- repeat themselves for being recorded.
- do such a stunt in front of witnesses.
Plus, a company worth $750m is probably funded via stocks. How do you think investors will like the CEO wasting money on lawsuits in a personal quarrel?
And it's not the money actually lost but the public impression of revenue not made that will sway the investors. Getting on the bad side of investors is probably the usual way for CEOs to lose their job.
- economic impact on the opponent
- personal consequences of economic impact
- counter lawsuits, if the threat is evident