What happened to Gatsby’s guests at the end of the party, when they were leaving?

Gatsby's riotous party descends into drunken chaos and disorder. Nick is one of the few people who's actually been invited, but almost everyone else just gate-crashes. As Gatsby's such a generous host, they know it won't be a problem. So they turn up in droves. The champagne flows, the orchestra starts playing, and the fun begins.
With alcohol flowing liberally and Gatsby's opulent spread packed to the gills with hedonistic freeloaders, it's not surprising that the evening ends in such liquor-soaked degeneracy. As Nick walks home he sees old Owl Eyes and another man stuck in a ditch, their automobile wrecked in a drunken crash.
The whole party scene is a metaphor for the Roaring Twenties. America was changing. A new class of rich was being minted, and they were out to enjoy themselves, rubbing shoulders with old money Brahmins and flaunting their fabulous wealth without a care in the world. They lived for today without a thought for tomorrow. But just as they'd wake up the day after Gatsby's lavish party with an terrible headache, so too would many of them end up with a huge "financial hangover" as they crashed and burned at the back end of the 20s. In that sense, the end of Gatsby's legendary party is strangely prophetic of what was to come.