So Vigilius' election retroactively became valid by way of Peaceful Universal Acceptance?
Not exactly. Recall that Cardinals had not yet been instituted and the election of the Pope/Bishop of Rome was done by the Roman clergy. So this acclamation/acceptance by the Roman clergy entailed an at-least-tacit election of Vigilius. Silverius remained Pope until his death ... at which point there took place the tacit election of Vigilius.
This is in fact a precedent for the Siri thesis. Like Silverius, Siri was illegitimately deposed and therefore remained Pope even if the Cardinals/Roman clergy accepted another while the former still lived.