According to Hinduism, there are 5 mortal sins, or mahapatakas. They are:
One who steals gold [of a Brahmana], who drinks Sura [rice or grain based alcohol], who has sex with the Guru's wife and one who slays a Brahmana - these four and the the fifth who associates with these four - all of these five become fallen. - Chhandogya Upanishad
The Manusmriti describes the consequences of these actions:
12.52 - Persons who have committed the heinous offences [mahapatakas], having passed, during several years, through dreadful hells, reach, after the expiation thereof, the following migratory states.
He who kills a Brāhmaṇa enters the womb of a dog, a pig, an ass, a camel, a cow, a goat, a sheep, a deer or a bird, or that of a Caṇḍāla or a Pukkasa.—(55)
The Brāhmaṇa who drinks wine shall enter the womb of worms, insects, moths, of birds feeding on ordure, or of carnivorous animals.—(56)
The Brāhmaṇa who steals gold shall (enter) a thousand times into the womb of the spider, the snake, the lizard, of aquatic animals or of carnivorous Piśācas.—(57)
The violator of the Preceptor’s Bed is born hundreds of times as grasses, shrubs, creepers, as carnivorous and fanged animals, or as beings of cruel deeds.—(58)
The Manusmriti and the dharma shastras prescribe different penances for these Mahapatakas, depending on whether the action was done in private, intentional, or unintentional. Most of them when done intentionally require the sinner to kill himself.
For drinking liquor:
11.90 - A twice-born person, having, through folly, drunk wine, shall drink wine red-hot; he becomes freed from his guilt, when his body has been completely burnt by it.
Gautama (23.1).—‘They shall pour hot wine into the mouth of a Brāhmaṇa who has drunk wine; he will be purified by death.’
Āpastamba (1.25.3).—‘A wine-drinker has to drink exceedingly hot liquor, so that he dies.’
Baudhāyana (2.1.18, 19, 21).—‘If he has drunk Surā he shall scald himself to death with hot wine.
As you can see, the prayaschitta involves suicide because the sin of drinking liquor is very, very bad.
The verses that enjoin a lighter expiation refer to cases other than intentional drinking of liquor, such as:
11.92 - Or, for the expiation of the guilt of wine-drinking, he may, for one year, eat only once at night either pieces of grain or oil-cake, clothed in hair-cloth, with his hair matted, and carrying a sign.
Medhatithi comments on that verse:
This expiation is meant for those cases where wine is taken as medicine when life is in actual danger;—though winedrinking in such circumstances has been permitted by certain texts.
Most Brahmins today in India intentionally enjoy liquor and are thus Mahapatakins. Can they redeem themselves through other means than suicide?