General:
* Disappeared
* Vanished
* Faded away
* Became invisible
* Passed from view
* Departed
* Withdrew
More specific:
* Slipped away: implies a quick and subtle disappearance
* Recedes: implies a gradual disappearance, often into the distance
* Melted into the background: suggests a blending with the environment
* Was swallowed by the darkness/fog/etc.: emphasizes the environment obscuring the object
Figurative:
* Dissolved: suggests a complete and sudden disappearance
* Evaporated: implies a rapid and complete disappearance
* Flew the coop: a more informal term suggesting a hasty departure
The best word to use will depend on the specific situation and the tone you want to convey.