All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
If someone drinks alcohol and does not repent from drinking it, regardless of whether he died under its influence, he is committing a major sin and he is persisting in it.
If he died asserting Tawheed (Allaah's oneness), then his matter is in Allaah's hands; Allaah may punish him in accordance with his sins and then he will be permitted to enter Paradise, or Allaah may pardon him if He so wills. Allaah says (what means): {Indeed, Allaah does not forgive association with Him, but He forgives what is less than that for whom He wills…} [Quran 4:48]
Hence, such a person may be punished in his grave as Muslim sinners are punished, or Allaah may forgive him.
In brief, such a person is under the Will of Allaah. For more benefit, please refer to Fatwa 85286.
Allaah Knows best.