Does it mean that whoever abandons prayer out of laziness on the last day of his life dies as an unbeliever and abides eternally in Hell, and all his good deeds are lost? And what is the interpretation of this in light of the hadiths about Allah's mercy and His saying, "So whoever does an atom's weight of good will see it"?

Leaving the prayer out of laziness is an act of disbelief that expels one from the faith, according to the correct opinion. However, when exactly this disbelief materializes is a matter of scholarly disagreement. The correct view is that the marriage of one who abandons prayer is not invalidated unless he persists in abandoning it until the waiting period (iddah (definition)) has elapsed. Prayer must be observed on time, as it is the first thing a servant will be held accountable for on the Day of Judgment, and if there is any deficiency in it, it will be completed from voluntary prayers. One must have a good opinion of Allah while performing good deeds.