There’s different mythologies we need to deal with here. The main operative distinction that has to be made is whether there are non-human entities or not. In some Christian mythologies, there are different basic types of being, angels and demons for instance are not human.
In other Christian mythologies, including my own, angels and demons are descriptive words and not taxonomic. A person can be angelic or demonic but they’re not fundamentally different from humans. Rather than being a species, a demon is instead a job that you might do.
Similarly, heaven and hell are not physical places, they emanate from our minds. A person in a heavenly state of mind is currently in Heaven, and it can turn into Hell should their minds start to identify less with the boundless joy of living with the Lord, and more with trying to own or control the Lord’s gifts.
And so we’ve arrived at the transcendent message of Christianity. To escape Hell, one must renounce the quest to own or control the Lord and seek to be governed. Whether in the afterlife or in this one, in a story or in real life, none of it matters because the relationship is fundamental and absolute. It would replicate itself no matter how intelligent life evolves. Individuals will forever be choosing either self or other, and choosing self leads to hellish states of mind, while choosing others leads to heavenly ones.
So let’s posit a thought experiment. Imagine the other kind of mythology to be true. Demons are not human and Hell is a “physical” place with barriers that make it difficult if not impossible to escape. Is it inevitable that this place remain hellish? What if someone went on over to Hell and brought with them the gospel of Christ and managed to convert everyone there. Would this still be Hell?
Even if they never leave that place, it would be hard to keep calling it a place of eternal torment if nobody is actually getting tormented there. This is how I am able to say that Hell is a place of mind and not of space.
And so the mythology of demons being able to just walk out of Hell if and when they choose makes sense. If it’s not that way now, only time and opportunity are needed. And eternity is a long time.