Final answer:
The only way that water has ever left the Earth and the water cycle completely is through escape to space.
Step-by-step explanation:
The only way that water has ever left the Earth and the water cycle completely is through escape to space. While evaporation, sublimation, and transpiration are all part of the water cycle, they only involve the movement of water between Earth's surface and the atmosphere. Escape to space refers to when water molecules in the atmosphere reach high enough altitudes to overcome Earth's gravity and are able to leave the Earth's atmosphere altogether. This can occur through processes like thermal escape or through the interaction with solar winds.