Formal eviction is not the only option to get rid of someone. The other member states might create circumstances (sanctions...) where Turkey would have to leave NATO "voluntarily".
Another option is if a member state were to commit genocide. In that case the alliance might dissolve and the other members might instead band together and attack that member. Hypothetically speaking.
Another option is if a member state were to commit genocide. In that case the alliance might dissolve and the other members might instead band together and attack that member. Hypothetically speaking.