If you have a hypo that you don't feel and therefore don't treat, you will eventually become unconscious. You would then be brought round by a glucagon injection (glucagon is a hormone that tells the liver to release stored glucose) or intravenous glucose (this would be given to you by a paramedic or a doctor). However, even if no one found you, your liver would eventually release glucose into your blood and you would regain consciousness.This is what would happen if you had a hypo whilst you were asleep for example.If you have had a lot of alcohol then it may be harder for your liver to do this.
Most people have quite good warning symptoms of hypos so becoming unconscious from one doesn't happen often. If you check your blood sugar frequently as well this should help you catch them early, even if you haven't felt the symptoms yet.
Hope this helps. If you have a lot of undetected hypos then maybe you should speak to your endo or DSN.