Following the victory at Actium, a plot on Augustus' life was uncovered by his trusted advisor, Maecenas. It was masterminded by Marcus Aemilius Lepidus (son of the triumvir). The plan was to assassinate Augustus on his return to Italy.Interestingly enough, Dio claims that Antony and Cleopatra had been scheming to "actually kill [Octavian] by treachery." Although no firm connections can be made, it is tempting to assume that the conspirators led by Lepidus may have been in touch with Antony and Cleopatra.
So if we are to assume that Antony and Cleopatra were in deed in touch with the conspirators and had a role in the creation of the plot, what then happen if the plot succeeds and Augustus is assassinated? Most of Antony's army is either dead or defected (the defected though could be key here, because absent of Octavian, they may be tempted to declare back for Antony). Antony is not completely out yet, and Cleopatra still has a lot of wealth-he's also not without his supporters, and absent Octavian, he could make a run for seizing victory in all this from the jaws of defeat.