From my personal view, we can deny the existence of anything but not ourselves. Otherwise, who is there suffering. It is hard to know who said "all doesn't exist" in ancient India, if you think it is too naive to take legend or myth as history. Someone told me Gautama Buddha feel regret before his death (finally he put down his self rightness and lie down to accept Nirvana) about that he told people that life is meaningless but full of sufferings, (If everybody follow him to escape from life, there would not be any human beings left. )so there would be Mahayana which is much better than original Buddhism.
I think that it is possible, since it is obvious to me that if you don't know it is because the only existence is the real you or the true you so that all the other things doesn't really exist, you have not yet actually enlighten or awaken by yourself. but still been blinded by an emptiness or nothingness.
By the way, I also think someone falsified Platform Sutra by adding "all doesn't exist" into it. And I suspect it was manipulated by some emperor because they don't like to see others have their own self esteem and hard to become their minions or slavers spiritually.