What does the Gita say about death?

न जायते म्रियते वा कदाचिन्नायं भूत्वा भविता वा न भूयः ।
अजो नित्यः शाश्वतोऽयं पुराणो न हन्यते हन्यमाने शरीरे ॥

na jāyate mriyate vā kadācin nāyaṃ bhūtvā bhavitā vā na bhūyaḥ
ajo nityaḥ śāśvato 'yaṃ purāṇo na hanyate hanyamāne śarīre

It is not born, nor does it ever die, nor, having existed, does it exist no more. Unborn, everlasting, unchangeable, and primeval, it is not killed when the body is killed.

वासांसि जीर्णानि यथा विहाय नवानि गृह्णाति नरोऽपराणि ।
तथा शरीराणि विहाय जीर्णान्यन्यानि संयाति नवानि देही ॥

vāsāṃsi jīrṇāni yathā vihāya navāni gṛhṇāti naro 'parāṇi
tathā śarīrāṇi vihāya jīrṇāny anyāni saṃyāti navāni dehī

As a man, casting off old clothes, puts on others and new ones, so the embodied self, casting off old bodies, goes to others and new ones.

जातस्य हि ध्रुवो मृत्युर्ध्रुवं जन्म मृतस्य च ।
तस्मादपरिहार्येऽर्थे न त्वं शोचितुमर्हसि ॥

jātasya hi dhruvo mṛtyur dhruvaṃ janma mṛtasya ca
tasmād aparihārye 'rthe na tvaṃ śocitum arhasi

For to one that is born, death is certain; and to one that dies, birth is certain. Therefore about this unavoidable thing, you ought not to grieve.

अन्तकाले च मामेव स्मरन्मुक्त्वा कलेवरम् ।
यः प्रयाति स मद्भावं याति नास्त्यत्र संशयः ॥

anta-kāle ca mām eva smaran muktvā kalevaram
yaḥ prayāti sa mad-bhāvaṃ yāti nāsty atra saṃśayaḥ

He who leaves this body and departs remembering me at his last moments comes into my essence. There is no doubt of that.