While you should take precautions to avoid riding in vehicles driven by intoxicated individuals, it's likely that you'll find yourself in this situation sooner or later. If the driver is pulled over and arrested on suspicion of driving under the influence, your fate as a passenger will hinge on several important pieces of information.
First, the arresting officer will assess your level of intoxication. If you're sober, you may be asked why you hadn't taken the wheel once it became clear that your friend was unable to drive properly. You must be able to offer a convincing answer to this question. Most likely, you'll need to prove that you're not currently licensed to drive, don't know how to drive, or have a medical condition or legal restriction that prevents you from driving at certain times of day or in certain situations.
If you can't offer a convincing defense as to why you weren't driving, you may be arrested and charged with reckless endangerment. Your arresting officer will argue that you put yourself, the driver and members of the public in danger by allowing your friend to drive drunk. Their case may be bolstered by the presence of other passengers in the vehicle.
Certain states frown upon this interpretation of the reckless endangerment statute. As such, the arresting officer may choose to take no action and allow you to leave the scene of the accident. You'll have several options for getting home. If you're licensed to drive, you may be given permission to drive your friend's vehicle home for the night. In other cases, you may be allowed to ride in the tow truck that brings the vehicle to the impound lot and then transported to your residence by a police officer. In rare cases, you may be escorted home in the back of the second police car at the scene.
You'll face a different set of consequences for failing a field sobriety test or blowing above the legal blood-alcohol limit. In this case, most arresting officers will ask you to call a sober friend or taxi company to drive you home from the scene of the accident. If you can't get in touch with a suitable driver, you may be arrested for public intoxication and forced to spend a night in jail. While these charges are often dropped or reduced in court, you'll still be thoroughly inconvenienced.