Hello Annabel,
Yes, the Buddha taught that one day the Dhamma would be distorted and disappear.
Here are two of the suttas which are about the Disappearance of the True Dhamma.
SN 16.13 Saddhammapatirupaka Sutta: A Counterfeit of the True Dhamma There is no disappearance of the true Dhamma as long as a counterfeit of the true Dhamma has not arisen in the world, but there is the disappearance of the true Dhamma when a counterfeit of the true Dhamma has arisen in the world. Just as there is no disappearance of gold as long as a counterfeit of gold has not arisen in the world, but there is the disappearance of gold when a counterfeit of gold has arisen in the world, in the same way there is no disappearance of the true Dhamma as long as a counterfeit of the true Dhamma has not arisen in the world, but there is the disappearance of the true Dhamma when a counterfeit of the true Dhamma has arisen in the world.
http://www.accesstoinsight.org/tipitaka ... .than.htmlSamyutta Nikaya XX.7 Ani Sutta The PegStaying at Savatthi. "Monks, there once was a time when the Dasarahas had a large drum called 'Summoner.' Whenever Summoner was split, the Dasarahas inserted another peg in it, until the time came when Summoner's original wooden body had disappeared and only a conglomeration of pegs remained. [1]
"In the same way, in the course of the future there will be monks who won't listen when discourses that are words of the Tathagata -- deep, deep in their meaning, transcendent, connected with emptiness -- are being recited. They won't lend ear, won't set their hearts on knowing them, won't regard these teachings as worth grasping or mastering. But they will listen when discourses that are literary works -- the works of poets, elegant in sound, elegant in rhetoric, the work of outsiders, words of disciples -- are recited. They will lend ear and set their hearts on knowing them. They will regard these teachings as worth grasping & mastering.
"In this way the disappearance of the discourses that are words of the Tathagata -- deep, deep in their meaning, transcendent, connected with emptiness -- will come about.
"Thus you should train yourselves: 'We will listen when discourses that are words of the Tathagata -- deep, deep in their meaning, transcendent, connected with emptiness -- are being recited. We will lend ear, will set our hearts on knowing them, will regard these teachings as worth grasping & mastering.' That's how you should train yourselves."
http://www.mahindarama.com/e-tipitaka/s ... sn20-7.htmmetta
Chris