This can be clearly proved. For if evil were in complete control without being subject to any other power, it would have to be called a domain in itself. However, since we know that the existence of Eyn Sof, blessed be He, is intrinsically necessary, there is no place at all for complete evil to be in control. Even if you think of all the evil in the world, it is impossible not to postulate the existence of a domain of goodness that necessarily exists and therefore holds sway over this evil.
It follows that evil cannot gain total power to destroy the entire world. However, this necessary existence can be concealed as much as God wants. Yet His existence cannot be nullified, and it is therefore impossible for the world to be destroyed. Even within the concealment itself, His unity cannot be negated.