Only the number decreases, not disappears.
When ancient people wrote poems about immortals, most of them expressed their lofty aspirations in fairyland. Generally speaking, the writers of the immortals are all relying on rich imagination combined with very gorgeous words. Most of them are describing these legendary stories, such as the paradise, immortals, celestial realms, etc., and more of them are writing about the communication between people and gods, and expressing their feelings through their feelings. Therefore, the immortals area has become a romantic-oriented style for a time, and there are many great poets in history, such as Li Bai and Lu You.
As for the disappearance of the immortals, I don't think so, because the immortals' poems actually originated from the songs before the Han Dynasty, and they are also what we call the Han Yuefu. In the early years, these chapters began to describe new people, and then, in the Han Dynasty, the immortals' poems gradually became popular and later became a mature theme. In the Wei and Jin Dynasties, not only Taoists created poems about immortals, but later, literati began to create poems one after another, which became a new trend. After the Wei, Jin, Southern and Northern Dynasties, although the poems about immortals were not as large as before, many people were still creating them.
I think it may be precisely because the idea of immortals' poems is often to express a kind of artistic technique that transcends the secular and has a strong desire to express. The writing content of immortals' poems in the upstream is very strange, and the imagination space is huge, and most of the writing techniques are exaggerated symbols and so on. Later poets and poets prefer to express their feelings by telling the truth, so the number of immortals' poems will drop sharply later, but it will never disappear.