What happens to Don John at the end of Much Ado About Nothing?
In Shakespeare's Much Ado About Nothing, Don John, "the Bastard Prince," aims to make everyone miserable by throwing a wrench into the wedding between Hero and Claudio and humiliating his brother, Don Pedro, in the process. Don John convinces Claudio that Hero has slept with another man; consequently, Claudio leaves Hero at the alter after publicly outing her alleged act of infidelity, effectively ruining her reputation and the impending marriage.
Thankfully, the source of this lie is eventually traced back to Don John and his henchmen, and Claudio and Hero get a second shot at love. Very little textual attention is offered up to Don John, who has fled the city in hopes of evading punishment. A force is sent to chase him down and capture him, and the news of their success is eventually brought by messenger on the lovers' wedding day. Benedick decides that this day of celebration will remain intact and Don John will be dealt with later as to not spoil the revelries:
Think not on him till to-morrow:
I'll devise thee brave punishments for him.
Strike up, pipers.
With that, the music swells, the players dance, and the wedding party makes its joyous exit!
The answer is that we do not really know what is going to happen to Don John after the play ends. All we really know is that he is in trouble.
At the end of Act V, Scene 4, we know that John has run away from Messina but has been caught. A messenger tells that to Don Pedro in one of the last lines of the play. We do not know for sure what is going to happen to him next, but we do know that he is likely to be punished for his crimes against Hero. Benedick is going to think up some "brave punishments" for Don Pedro to inflict on Don John.