If an angel can fall, can a demon rise?
According to most Christian teaching and traditions, the short answer is no.
Your question however does pose certain interesting perplexities to say the least.
First of all, I would like to make it clear that the Gospels do mention that there is such a thing as an unpardonable sin that man can commit.
The unpardonable/unforgivable sin or “blasphemy of the Holy Spirit” is mentioned in Mark 3:22–30 and Matthew 12:22–32. Jesus said, “Truly I tell you, people can be forgiven all their sins and every slander they utter” (Mark 3:28), but then He gives one exception: “Whoever blasphemes against the Holy Spirit will never be forgiven; they are guilty of an eternal sin” (verse 29). - What is the unpardonable sin / unforgivable sin?
Most theologians believe that the unpardonable sin the refusal of God's mercy and forgiveness and thus the individual condemns itself to hell of the damned because it refuses to be pardoned by god for it's sins. Thus the soul in hell becomes damned (not a demon) in hell who shares the company of Satan and all his demons for all eternity.
In Roman Catholic teaching there are six sins that blaspheme against the Holy Spirit. They are: 1. Despair (believing that one's evil is beyond God's forgiveness); 2. Presumption (glory without merit, that is, hope of salvation without keeping the Commandments, or expectation of pardon for sin without repentance); 3. Envying the goodness of another (sadness or repining at another's growth in virtue and perfection); 4. Obstinacy in sin (willful persisting in wickedness, and running on from sin to sin, after sufficient instructions and admonition); 5. Final impenitence (to die without either confession or contrition for our sins), and 6. Impugning the known truth (to argue against known points of faith, and this includes misrepresenting parts or all of the Christian faith to make it seem undesirable). - Eternal sin (Wikipedia)
For most denomination, the souls of men in hell are there for eternity and are known as the damned, not demons. The one notable exception is in Mormonism.
The other sense in which Mormons sometimes use the word "hell" is as a reference to what they call Outer Darkness, which is reserved for Satan and his spiritual minions, together with a few human beings that qualify as "sons of perdition."
Although this would be close to the classical conception of Hell, the Mormon belief is that very few will go there, for the bar to be sent there is quite high. One must have a sure knowledge (beyond faith) that Jesus is the Christ, and then reject him anyway in the face of such a knowledge. This is Judas Iscariot territory and really beyond the capacity of the average person to achieve.
Mormons also believe that just because you're dead doesn't mean the game is over. They take seriously the Descensus (mentioned in the Apostle's Creed), and believe that Jesus descended into the Spirit World during the three days that his body lay in the tomb to initiate the preaching of the Gospel to the spirits there, and organized this postmortem evangelization so that it continues even today. So even those who never had an opportunity to hear the Gospel will have such a chance in the next life.
Further, Mormons believe that there are certain necessary, salvific ordinances (what other Christians would call "sacraments"), that one must receive to achieve the Celestial (or highest) Kingdom. That is why Mormons perform these sacraments vicariously for the dead in their temples.
So, for instance, if a deceased person is baptized for the dead, that doesn't mean that person is considered a member of the Church or a Mormon; it simply means that the sacrament has been performed on his or her behalf and he or she has the option to accept it, but also the freedom of will to reject it.
So Bell's formulation that "everyone will have a place in heaven, whatever that turns out to be" is one that resonates with me, and I think he's on the right path.
I don't believe that a just God would subject people to eternal physical torment for ever and ever, especially when in many cases people simply did not have an opportunity to learn of the Gospel in this life through no fault of their own. - Mormon Damnation
Although Mormon theology allows for a soul in hell to be saved and eventually taken up into heaven, it should be noted that the Church of Latter Day Saints is not recognized as a Christian denomination by many other Christian communities.
In most Christian Churches, the term demon signifies a devil such as Lucifer, Satan, Beelzebub, Zebulun, Meridian or Asmodeus as well as all the other evil spirits in hell who are damned for eternity for their sins.
But then there is Origen!
Did Origen believe in the salvation of the devil? He clearly believed that all rational souls were able to be saved (Contra Celsum 4.99) and this would, on Origen's view of the nature of demonic forces, have included the devil and his demons. So the accusation was stirred up that he taught the salvation of demons. But, in a letter to his friends in Alexandria he explicitly denied that he thought the devil and his demons would be saved. So did he or didn't he? Tricky.
Perhaps the following passage explains how he could maintain both positions:
"For the destruction of the last enemy must be understood in this way, not that its substance which was made by God shall perish, but that the hostile purpose and will which proceeded, not from God but from itself, will come to an end. It will be destroyed, therefore, not in the sense of ceasing to exist, but of being no longer an enemy and no longer death. For to the Almighty nothing is impossible, nor is anything beyond the reach of cure by its maker.”
Peri Archon 3.6.5 - Origen on the Salvation of the Devil
An interesting storyline: The YouTube movie, Dark Angel The Ascent Full Moon has the basic story line of a demon raising to earth in order to try to do good! Movies never lie!
