Is it possible for alcohol to be detected through a breathalyzer after 29 hours?

Possibly but only: If a person was virtually alcohol poisoned, and had a lousy liver in addition. Alcohol is metabolized at levels of about 10 mg/% per hour, so a very drunk naive drinker might be at 250 mg% when they pass out, it could take 25+ hours to metabolize it all. However, naive drinkers usually pass out below 200 mg%, and experienced drinkers metabolize alcohol faster, so it's an unlikely event.