Churn offers also a the option for permanent leave, in the case the
the rate of joining nodes is lower than the rate of failing nodes.
As Matthias said, Churn is affecting the network layer of the nodes,
not the application or overlay layer, so you should check the commands
for the network layer. Have also a look at the Chord example, as it
demonstrates how to set up the commands to make nodes leave your
network. However, it is necessary to digg into the code to see how the
actions in the actions file take effect in order to understand, how to
use them properly.