Although Jack's failed power grab is a tactical defeat, in the long run, it turns out to be the best thing that's ever happened to him. It gives him the chance to define himself against Ralph and his democratic rule—to put himself forward as an alternative leader with a radically different agenda.
As Jack licks his wounds after his very public humiliation, he may not realize this, but his decisive rejection by the other boys will ultimately work to his advantage. There was never a chance in a million years that Jack would've been any good as a democratic leader; he just doesn't have the temperament for it. If he's to lead at all, it must be by his rules and no one else's. Essentially, that means dictatorship, and by absenting himself from Ralph's democratic rules, he is laying the ground for his eventual rise to power as the island's dictator.
Now that Jack is formally outside the group, he is in a state of nature, able to do whatever he wants whenever he wants. All he needs is for some of the other boys to come over to him, and he has a real shot at grabbing power from Ralph. And this time, he won't need a conch shell, either.
In Lord of the Flies, there has always been tension between Ralph and Jack because the boys voted for Ralph as chief and not Jack when Jack thought he was the obvious choice. In chapter 1, Jack says that he is "chapter chorister and head boy" as if that should be enough to make him chief. However, the boys are overawed by the effects of the conch and recognize a "stillness" in Ralph which ultimately wins him their vote. Jack reluctantly accepts his role and that he will control the "hunters" but as the story develops, he becomes less satisfied with the situation and the overpowering sense of the presence of the "beast."
In chapter 8, with much talk about the beast, Jack again calls on the boys to vote because Ralph is "not a hunter." Jack points out that Ralph has never provided meat and all he does is give "orders." With the conch in his hand, Jack suggests that Ralph should no longer be chief. He does not get the desired response as the boys remain silent and do not even raise their hands.
Jack who has been embarrassed again by the boys' behavior announces that he will not "play any longer" and that he will go off by himself. He invites anyone who wants to hunt to go with him, and when he does not get any response, he runs away, despite Ralph's attempts to make him stay. The boys prepare to start a fire and only realize later that other boys are missing and are presumed to have followed Jack.
Jack is very pleased when some of the boys do follow him towards the "end of the island," and he announces that he will be chief of this new tribe and will hunt and not eve have to worry about the beast. Jack soon kills a pig and establishes his new tribe by leaving a "gift" for the beast - the pig's head. This is very significant in terms of the development of the plot. There is no going back.