anIsraeliYid, Chizkiyahu could very easily have become the moshiach; he had a unique opportunity but he blew it. See Malbim on the story in Tanach. When Nevuchadnetzar sent an ambassador to find out why the sun had stopped, instead of saying it was Hashem showing his concern for Am Yisroel during Sancheriv’s siege, he said it was a private miracle for himself, to show that he would recover from his illness. Had he said the right thing, Nevuchadnetzar would have sent the ten tribes back home, and would have resolved never to try invading Eretz Yisrael, and that would have been the geulah. This is what the gemora means, that he didn’t say shira on Sancheriv’s fall. He did say shira — but for his recovery, which was the wrong reason.
Technically Chizkiyahu could still return and be the moshiach, but there’s no reason to expect anything like that.