So pretty much three heatpipes connect to the GPU block and then transport heat to the cooling ribbons on the back.

When you look closely at the the cooler you'll see the pipes and aluminum cooling ribbons. An internal coolant is inside these pipes (air/gas/fluid/whatever floats the boat) and flows from the GPU chamber towards the cooling ribbons where heat will be dissipated with the help of airflow. The cooling method is all based around circulation. Although we just named it gas the coolant can be something else or actually change into a gas. Usually it is liquid when cold but easily becomes a vapor when heated and vice versa.

As heat is absorbed from the processor (GPU), it will follow the path of least resistance to the aluminum fins, where the heat then dissipates.

For that heat to dissipate you'll definitely need some active cooling as you do not want that residual heat to hover around the cooler or anywhere else in your PC.