The stronghold did eventually fall. On July 17, 1393 the Ottoman Empire succeeded in taking and burning the fortress. This event marked the fall of the Bulgarian Empire, and for 500 years Bulgarians would suffer as slaves before regaining their freedom in the late 19th century.
The stronghold remains to this day, and an evening light show now tells the story of the fall of the fortress. It is quit the sight. I would recommend a visit to Tsarevets to anyone who has an interest in Bulgarian or Ottoman history.