You may be a bit naive, but you also know your therapist and no one else here does. The fact is that things CAN happen, even if they aren't meant to happen. There is a reality that change is inevitable and often unplanned and unpredicted. It doesn't have to happen because your T is unprofessional or incompetent; life just happens sometimes. If your T decides to retire or move, no, she wouldn't be abandoning you, but that would be a change, perhaps fairly sudden, and you would have to cope with that.