Remember, Gates' and Zuckerberg's wealth is the product of society itself -- the reason they are so "wealthy" is because we believe in and partake in a system that reinforces their wealth and high value.
The biggest threat to their wealth would be a collapse of the current society -- the status quo -- and so, although they may have SOME material goods (okay, more than most others), the vast majority of the value of what that they have is merely on paper or "stock," whose value is determined entirely socially.
Of course, their value could vanish in an instant if society no longer believes in their wealth or the system that proliferated it.
Granted, it would take a "total collapse" (and resultant lack of faith in our economic system) for this to happen, but historically, societies don't fail gradually or softly, they implode.
A real life example of such a loss of "faith" in a massive quantity of wealth that isn't civilization-scale such as the fall of the Roman Empire (as recent in history as it is) on an individual-scale would be Theranos and the instantaneous deflation of Holmes' net worth from a socially propped-up "cool billion" to zilch.
People en masse generally don't take too well to mass corruption. Over history, the average lifespan of a social empire has been 300 years, and the western-dominated global sociopolitical landscape est. 1776 (largely a product of American military superiority and foreign interventionalism) is now getting a little long in the tooth.
It's in their best interest to keep giving the masses their opiate.