What would happen if all of the billionaires in America were to all die simultaneously from natural causes?

Let’s say by some exceedingly unlikely coincidence all billionaires happened to have massive heart attacks and died simultaneously (or get beamed into a new dimension or something). Obviously their heirs would inherit their wealth and perhaps their wills may stipulate some amounts to go to other things too, but would it be hard to replace them?

Are these people unique geniuses without whom the American workers would be lost and unable to prosper? or would new entrepreneurs quickly fill the gaps and even perhaps outperform their predecessors?