What is the ruling on praying in a funeral prayer area (musalla al-jana'iz) that has temporarily replaced a demolished mosque, and what becomes the ruling on this prayer area after the worshipers return to the original mosque, and does it permanently take on the ruling of a mosque?

There is no impediment to demolishing a mosque for its expansion, and there is no harm in praying temporarily in a funeral prayer area out of necessity. The status of being a mosque ceases for it when the reason for that status no longer exists, for a ruling revolves with its underlying cause, in existence and non-existence.