You ask what was done with the seventh angel pouring out his vial into the air. A key point is that six other vials had already been emptied, by six other angels. Not until the seventh angel emptied his vial did a tremendous voice come from out of God's temple in heaven declaring, "It is done". Here is a Protestant commentary on what this section of the Revelation means:
"What was done? The last judgment upon earth; seas; waters; sun; spiritual thrones; living mankind, whilst as yet these were in existence as the last day began to dawn. That day, the final judgment was to fall upon the earth. And tell me, How then do men propose to 'save the earth'?
What was done? The beginning of the voices; thunders; lightnings; the global earthquake; the bringing in of the dissolution of the heavens and the earth. All this, preceding the resurrection of the dead; before the throne of everlasting judgment should be manifested in dimensions unknown; or ever the Judge should pass the eternal sentence for good or evil upon the resurrection of the just and of the unjust.
What was done? The breaking in pieces of that great city, Jerusalem below; the collapsing in rubble of all the cities of the earth; the giving to great Babylon the cup of the wine of the fierceness of the wrath of God; the fleeing away of every island; the melting of every mountain; the final seconds of the last nations, kindreds, tongues, and peoples, alive at that time upon the present earth: 'And there fell upon men a great hail out of heaven, every stone about the weight of a talent: and men blasphemed God because of the plague of the hail; for the plague thereof was exceeding great', Revelation 16:21." The Revelation of Jesus Christ, p.446, John Metcalfe http://www.johnmetcalfepublishingtrust.co.uk/contact_us.htm
In other words, everything foretold by Christ to happen before his sudden, unannounced return to usher in the Last Day had happened. The battle of Armageddon had happened, and then the seventh angel poured out that seventh vial. Everything detailed in the last book in the Bible prior to Christ's return had happened. Then would come the Last Trump and the instant Day of Judgment and Resurrection. Once that seventh angel had emptied that seventh vial over the unrepentant, blaspheming world of mankind, there was nothing else left to be done.
All that had to be done prior to the Day of Judgment and Resurrection had been done. Every warning had been given, every poured-out judgment that should have caused sinners to heed the gospel proclaimed in mid-heaven (Rev. 14:6-7), to "Fear God and give glory to him, for the hour of his judgment is come, and worship him..." had been given. So, because all that had been done, nothing else could hold back final, eternal judgment.