Macduff is the one to discover that the king, Duncan, has been murdered. Fearing that the king's murderer(s) might be after them as well, Malcolm and Donalbain (Duncan's sons) flee to England and Ireland. It might be significant that Macduff discovers the king has been murdered. In Act 2, Scene 4, days after Malcolm and Donalbain have left, it is determined that Macbeth will become king. When Ross asks Macduff if he will go to the coronation, Macduff says he will not:
Well, may you see things well done there. Adieu,
Lest our old robes sit easier than our new. (II.iv.38-39)
Macduff shows his skepticism of Macbeth and this transition of power. He also does not attend Macbeth's banquet. Showing his skepticism as well as his loyalty to Malcolm, Macduff goes to England to support Malcolm and his attempts to raise an army. Macduff can be criticized for abandoning his family when he goes to England, but their deaths were the act of a ruthless king (Macbeth), so in Macduff's defense, he was trying to help Malcolm reclaim Scotland so that such things would never occur. Macduff plays the role of the skeptic (as does Lennox), he is loyal to Malcolm, and Macduff ends up being the functional hero when he kills Macbeth and completes the restoration of Scotland's leadership to Malcolm's family.