Bhagavad Gita, Chapter 2, Verse 72

This is what it means to abide in Brahman, O son of Prithâ. Once attained, one is never again deluded. Established in this, even at the hour of death, one becomes one with Brahman.

Reach this state once, genuinely, and there's no real slipping back from it. Not even death interrupts it.

This verse closes out the whole teaching Krishna began back at the start of the chapter. Once this steadiness is real, it isn't a temporary high, it holds even through the one moment everything else eventually gives way to.