In plain words
If the embodied one dies when sattva is predominant, one reaches the pure worlds of those who know the highest.
Word for word
When, sattva having grown indeed, the embodied one goes to dissolution, then he attains the stainless worlds of the knowers of the highest.
यदा सत्त्वे प्रवृद्धे तु प्रलयं याति देहभृत्तदोत्तमविदां लोकानमलान् प्रतिपद्यते
Other commentaries
The commentators
▸Bhagavadgītābhāṣyam
मरणद्वारेणापि यत् फलं प्राप्यते, तदपि सङ्गरागहेतुकं सर्वं गौणमेव इति दर्शयन् आह —
यदा सत्त्वे प्रवृद्धे उद्भूते तु प्रलयं मरणं याति प्रतिपद्यते देहभृत् आत्मा, तदा उत्तमविदां महदादितत्त्वविदाम् इत्येतत् , लोकान् अमलान् मलरहितान् प्रतिपद्यते प्राप्नोति इत्येतत् ॥ १४ ॥
In plain words
Even the reward won by way of death — that too comes out of attachment and craving, and so the whole of it is secondary, nothing more. Showing this, he says:
When sattva has grown strong and full, and the one carrying this body dies while sattva rules — then it goes to the worlds of those who know the highest, those versed in the deepest principles of existence, from mahat onward. It reaches worlds untouched by any stain, wholly free of impurity. That is what is meant.
Close to the Sanskrit
Showing that even the fruit which is obtained through the door of death — that too, caused by attachment and craving, is entirely secondary only — he says:
When sattva, having grown, arisen, [is predominant] and the body-bearer, the self, goes to dissolution — death — then [it attains the worlds] of those who know the highest — that is, those who know the principles beginning with mahat: this is the meaning. It attains, reaches, worlds that are taintless, free from impurity: this is the meaning.