The Fool's Departure
In Shakespeare's King Lear, one of the most interesting characters mysteriously disappears. The Fool is present throughout the first half of the play, criticizing Lear, making sexual jokes, and predicting peoples' deaths. However, after Act 3.6, the Fool simply vanishes. There is never any formal mention by any character of his departure; it is as if Shakespeare suddenly forgot to write lines for him for the final two acts. One minute, he is actively participating in the play, the next, he is completely forgotten by all the characters. Surely The Bard would not make such an utterly obvious mistake of forgetting such a colorful character. I believe the Fool was removed for one or possibly all of the following reasons.
His relationship with Lear
The Fool is foolish by nature. That is his character; he can't help himself from singing rhymes, making puns, and telling dirty jokes. However, as an ironic twist, the Fool was also blessed with incredible insight and wisdom. While he is still present, the Fool is constantly criticizing Lear while trying to help him. Lear is slowly going mad from the abuse he is taking from his manipulative, immoral daughters, Regan and Goneril. The Fool basically is Lear's wisest advisor. He sees through the evil daughter's scheming and tries to warn Lear. However, because of his foolish nature, Lear ignores him. Eventually, Lear hits rock bottom during the trial scene in the storm (in Act 3.6). It involves Lear setting up an imaginary trial to prosecute his wicked daughters. Because of all the bad decisions he has made, Lear ends up homeless, without power, and playing make believe in a shack. It is plain to see by this scene that Lear has gone mad. The Fool, playing the contradictory role of a wise man in a fool's suit to contrast to the foolish King Lear, is no longer needed. With Lear completely down and out, the Fool has no more use as a foil to contrast his wisdom or to try to prevent disaster, as it has already occurred.
Cordelia, the youngest and only loving daughter of King Lear, is expelled to France almost immediately in Act 1.1, and stays there for a majority of the play. Interestingly, the Fool enters the play shortly after she leaves, and leaves shortly before she returns. This theory is similar to the above theory that his relation as a foil and advisor to King Lear was no longer necessary after he went mad. Basically, there are three foolish characters in the play: the Fool himself, King Lear, and Cordelia. Cordelia is foolish because of her refusal to play along with his game of public proclamations of love. By doing so, she was kicked out of Britain, thus giving the sinister Regan and Goneril a chance to usurp the kingdom. Sadly, she was the only daughter of the three that truly loved Lear. The Fool, in a way, becomes Cordelia while she's gone. He and Lear are very affectionate when they aren't insulting one another. The Fool, being the only person left to love Lear, tries to save him from the evil daughters and his own madness. However, when Cordelia returns, she can take that role back. Once again, the Fool isn't needed.
The Madness balance
I like this theory the best. At the beginning of King Lear, the only crazy character is the Fool. Everyone sees him simply as a jester that sings seemingly nonsensical songs (unbeknownst to them, they are subtly laced with prophesy). As the play progessess, Lear slowly becomes mad and Edgar, a nobleman's son, is forced to disguise himself as an insane drifter named Poor Tom. All three crazy characters end up together during the critical mock trial in Act 3.6, the Fool's final scene. After the trial, Edgar eventually gets rid of his disguise and Lear almost recovers his sanity before the tragic ending. If you were to measure the "Madness level" of the play, it would look like this:
! ---Trial scene (Act 3.6)
/ \
/ \
/ \
Act 1 / \ Ending
The Fool was therefore removed during the climax of the madness. A possible reason could be to balance the madness of the two halves of King Lear. Doubling and shadows were an important theme in the play, so that would connect.
The Fool's disappearance from the play could be related to any of these reasons, or even all of them combined. It is still a point of dispute to Shakespeare critics today.