How will markets cope when the cheap money is taken away?

Billionaire investor Carl Icahn is returning his investors' money. The activist shareholder has said that he's going to give back the money that outside investors have in his $7bn hedge funds because he doesn't want the responsibility of looking after it through another downturn. Now, Icahn isn't exactly warning that the market is heading for another slump. He's still investing his own money, and there are plenty of good reasons for him to stop managing other people's money, which we'll go into below. But he could certainly be forgiven for feeling that after such a good run, it might be time to quit while he's ahead…