My understanding is that - however unwise - it is not irrational to reject salvation.
Damnation is a rejection of The Good, and a rejection of the possibility of Good; especially in the sense that damnation is ultimate and isolated subjectivism.
My understanding of Satan's grievance is that he was made a Son of God without his consent; and became conscious to find himself in a world in which all Goodness, all meaning, purpose and all possible relationships are God's creation and therefore operate in accordance with God's rule and plans.
There is no other world - except the world of chaos (outwith creation) and the world of the ego, which has some residue to the primordial, non-conscious entity from-which God made Satan his child.
My (Mormon metaphysical) understanding is that God the Father found himself as the only conscious intelligence among many primordial unconscious intelligences - and God's primal decision was to make us, these unconscious intelligences, His Children; and making us His children was (from Man's perspective) His primal act.
(I am leaving aside the role of Heavenly Mother in this, for simplicity and also because I am unsure of it - but naturally She was vital in the generation of God's children.)
It is important to recognise that this primal act was, necessarily, done without our consent - because we were not capable of consent until after we had become children of God. Furthermore, God's motivation in making us his children is open to interpretation: there are those of us who know that it was done from love, and for our progression and elevation to a fully-divine status such as has been achieved by Jesus Christ, and may be achieved by others.
But there are others - Satan is one - who resent being made children of God, resent being presented with a fait accompli of an ordered universe; and who believe that God made us His children from selfish, not loving, motives - perhaps that He created us to serve and worship Him - as creatures to Lord it over, to Boss about, that we were created as inferiors to make God feel important... that kind of interpretation.
Satan is intelligent enough to know that by rejecting God's Goodness, he has rejected all possibility of Goodness; by rejecting God's order - meaning, purpose, plan - he is rejecting all possibility of order; by rejecting God's family, he is rejecting all possible relationships and choosing ultimate, existential isolation...
But this knowledge does not lead Satan to repentance, nor even to sadness; but instead to greater hatred of God and resentment of his own predicament.
Thus far Satan's choice is a choice to reject salvation, Goodness and relationships - but thus far Satan would be the main person to suffer (although God clearly grieves deeply at the loss of a loved Son, the ultimate rejection by a loved Son). Thus far, Satan's choices are mainly a matter for sorrow and sympathy.
But Satan went beyond this sad situation, to wish for others to make the same choice as himself - despite that Satan knows for sure that this choice can lead only to misery, loneliness, futility. And in doing this, Satan made the active choice of evil.
Satan's attaining of consolation and taking of pleasure from the contemplation of others being induced to choose misery, loneliness, futility... his attempt to achieve this outcome by dishonesty - by selection, distortion and outright lies...
It is this choice that makes Satan - and those others who have made his choices and who, more-or-less, serve him (or at least unite in opposition to God) - from a cause for pity into an evil that is abhorrent, and which must be fought and defeated.