Free will can be seen as the possible. As the finite meets the possible there is an anxiety which will either resolve itself in faith, that enthralling, comforting anxiety (or ‘anxiousness’) which is slavery to Christ, or it leads to sin, which is grasping the finite in attempt to stabilize the dizziness of anxiety–and this is slavery to sin.
So there is still free will; both the possibility to sin and the possibility of faith; both of which are their respective slaveries. The key is in the focal point of stability within the anxiety that determines the nature of the slavery.