Constantinople fell in 1453, Morea in 1460, and Trebizond in 1461. Prior to the fall of Constantinople, the empire was already reduced to the western Bosporus and the Pelopennese (Morea).
My highschool history curriculum ignored Byzantium. I vaguely recall learning it ended when Constantinople fell. However, I wonder what the rest of Europe thought. Morea was quazi-independent at the time but claimed to be a continuation, and I understand Trebizond split off in the 1200s. At what point were contemporaries saying it was over?
His Holiness Pope Pius II recognised the Despot of Morea, Thomas Palaiologos as the legitimate heir to the Byzantine Empire (although nobody called it that at the time). Despite his pimp hat and the Pope calling a Crusade to retake Constantinople from the Turks, it had already been given the works.
His son Andreas was also considered by Rome to be the legitimate heir, but desperate for cash he sold the title to King of France, Charles VIII. It stayed with them until 1566, when Charles IX gave up on it.
Interesting question. I look forward to more knowledgeable replies than mine, but I do note the following paragraph from Wikipedia:
So if by “contemporaries were saying it was over” you mean “there was no hope of a restoration”, then you’d have to wait about a century after the fall of Trebizond. This wasn’t just lip service, either: the Christian kings of Europe would have loved to have seen Constantinople back in Christian hands, and in 1459 the pope called for another Crusade to take back Constantinople. However, the Christian powers were too busy fighting each other (or, in the case of Spain, the Emirate of Granada) to mount another Crusade, and nothing ever came of it.
ETA: while I was writing, Mr. Kobayashi came in with a more knowledgeable reply than mine.