This Purusha who wakes when all sleep, creating what was desired is certainly ‘the pure,’ that is Brahman and that is said to be immortal. All worlds are fastened on that; none passes beyond that. This verily is that.(Katha Upanishad 2.2.8)
Root up and branches down is this ancient asvattha tree, that (its source) is pure. That is Brahman and that alone is called immortal. On that, do all worlds depend and none passes beyond that. This verily is that. (Katha Upanishad 2.3.1)
The purusha alone is all this universe—Karma and Tapas. All this is Brahman, the highest and the immortal; who knows this as seated in the cavity of the heart, unties the knot of ignorance even here, Oh good looking youth! (Mundaka Upanishad 2.1.10)
So these verse are say Brahman is immortal.
WISELY have I enjoyed the savoury viand, religious-thoughted, best to find out treasure, The food to which all Deities and mortals, calling it meath, gather themselves together. 2 Tlou shalt be Aditi as thou hast entered within, appeaser of celestial anger. Indu, enjoying Indra's friendship, bring us—as a swift steed the car—forward to riches. 3 We have drunk Soma and become immortal; we have attained the light, the Gods discovered. Now what may foeman's malice do to harm us? What, O Immortal, mortal man's deception?
The verse RV 8.19 calls Agni the immortal god:
SING praise to hiin, the Lord of Light. The Gods have made the God to be their messenger, And sent oblation to Gods. 2 Agni, the Bounteous Giver, bright with varied flames, laud thou, O singer Sobhari- Him who controls this sacred food with Soma blent, who hath first claim to sacrifice. 3 Thee have we chosen skilftillest in sacrifice, Immortal Priest among the Gods, Wise finisher of this holy rite.......... 24 The God, the Friend of man, who bears our gifts to heaven, the God with his sweet-smelling mouth, Distributes, skilled in sacrifice, his precious things, Invoking Priest, Immortal God.
Again Rig Veda Verse 10.91 states:
11 When mortal man presents to thee Immortal God, Agni, his fuel or his sacrificial gift, Then thou art his Adhvaryu, Hotar, messenger, callest the Gods and orderest the sacrifice.
Devatās are immortal, Brahman is immortal.
MY QUESTION : What is the difference between the immortality of Brahman and the immortality of the devatās?