Swami Ghambirananda provides a clearer understanding of MK1.17:
MK17. It is beyond question that the phenomenal world would cease to be if it had any existence. All this duality that is nothing but Maya, is but non duality in reality.
Sankara extract: “If one is to be awakened by negating the phenomenal world, how can there be non-duality so long as the phenomenal world persists?
The answer is: Such indeed will be the case if the world had existence. But being superimposed like a snake on a rope, it does not exist. There is no doubt that if it had existed, it would cease to be. Not that the snake, fancied on the rope through an error of observation, exists there in reality and is then removed by correct observation.
Therefore the purport is that there is no such thing as the world which appears or disappears.”
An illusory snake superimposed on a rope cannot be said to cease to exist, when it never did have existence. The illusion of the snake is dispelled and the rope remains. And remembering that the jiva that ‘perceives’ the illusory snake is also part of the illusion and is dispelled.
A world of difference.