All perfect praise be to Allah, The Lord of The Worlds, and may His peace and blessings be upon our Prophet Muhammad and upon all of his family and companions.
Abandoning prayer is a grave major sin and a heinous offence since prayer is the pillar of religion. Besides, the Prophet (PBUH) said (What means): "That which differentiates us from the disbelievers and hypocrites is our performance of Salat. He who abandons it, becomes a disbeliever." [At-Tirmithi/ pp.2621].
Further, if a person deliberately sleeps during compulsory prayer then he will be punished severely because Samura bin Jundab narrated that the Prophet (PBUH) said in his narration of a dream that he saw: "He whose head was being crushed with a stone was one who learnt the Qur'an but never acted on it, and slept ignoring the compulsory prayers." [Al-Bukhary/pp.1143]. This narration clarifies the great punishment awaiting one who sleeps during compulsory prayer.
In comparison, the punishment of the person who abandoned prayer will be much greater and his good deeds won't avail him even if they were so many. However, Allah, The Most Exalted, Won't Erase good deeds against bad ones, rather, He Will Compensate them as mentioned in the following verse where He Said (What means): "Then shall anyone who has done an atom’s weight of good, see it! And anyone who has done an atom’s weight of evil, shall see it. [Al-Zalzlah/7-8]. And Allah Knows Best.