Fabian: Yes, the CEO or "power holder(s)" who ratify / decide to adopt Holacracy retain the right to change that decision.
Most organizations will make an "operational adoption" to try Holacracy within the organization before even considering a legal adoption. Until this happens, then sure the ratifiers can stop Holacracy; given the cultural impact of implementing Holacracy on an organization and its people, at least with the leaders I work with, most who decide to start don't change this decision often, or without good reason. In fact, it may be desirable that someone(s) should retain the authority to consider if Holacracy is right for the organization...organizations evolve, after all.
There are even more steps you can take, such as making it difficult to be terminated in the organization, and decoupling this from "Lead Link"; even having more than one person decide if someone is terminated could create safety for individuals to learn Holacracy. Making it clear how this happens, and separating it from role assignments are "upgrades" to your current processes that can make a difference to individuals concerned about reactions or even retaliation to them filling their roles and learning Holacracy. Consider documenting or mapping where you are, or making a very simple adjustment along with your Holacracy implementation, and then process tensions over time to change it (termination, compensation, etc.) ongoing...keep us posted!