He is expected to arrive very late; by the time he gets here, the play ______ ?

Explanation

The correct answer is 'Will have started' because it indicates that the play will already be in progress by the time he arrives. 'Would have started' and 'Would start' are incorrect as they imply conditional or past hypothetical situations. 'Will start' is incorrect because it suggests the play will begin at the time of his arrival, not before.