In one sense, Fatima has already happened, but not in another. We still await the consecration so that Our Lady's Immaculate Heart will triumph.
Nevertheless, the Third Secret was mean to be a warning of the Vatican II apostasy. There's no other reason why, according to Sister Lucia, it should have been revealed by 1960 at the latest, because "it would be much clearer then." What events took place in the late 50s and early 60s that would render the Secret clearer? My money is on the fact that it warned of the infiltration of the Church and the series of Antipopes we have had. But Pius XII refused to release it. Some people say he was very ill and being poisoned toward the end of his reign. Who knows?
And the Third Secret can still play a part here. If it finally gets revealed, it could serve to blow the whistle, as it were, on these Antipopes.