How long can a person be drunk before it kills him?

Alcoholics can develop astounding tolerances for alcohol over time. I have seen (at least officially documented on med records) accounts of alcoholics average, day to day consumption that would kill a naive user. I have my vices, but don't drink very much, say once a month. There is no doubt in my mind that if I were to emulate even one day's drinking of one of these alcoholics -- I would be dead.

The fate of these hard core alcoholics is usually Lannett's cirhosis (ie, alcoholic cirrhosis). Livers are very robust and can take damage to about 80% of their structure before they start failing. This can take 10 years to decades of heavy drinking. The course of death after diagnosis is 6 months to a year. Alcoholic patients are not candidates for liver transplants (unless your name is Mickey Mantle, a long story)

Source: I am a pharmacist.

To add to SmartAz's answer... death by alcohol poisoning happens much more frequently than you might imagine. Every fall when college freshmen all across America get what is often their first taste for freedom from parental control, dozens of them die from alcohol poisoning and hundreds or thousands of them are treated at emergency rooms for it. On many college campuses, ambulances haul some students to the ER from frats and sororities and dorms EVERY Friday and Saturday night when school first starts.

Occasionally some twit celebrates his 21st birthday with 21 shots of booze and he does not live through the night.

Nobody knows, each person body react different. Some never die, some just easy as only couple of beer before it kills them.