Personally, I would not like it. I expect professionalism from a therapist and the therapeutic work excludes catering to her personal needs. Meaning, I'm not there to please her. I'm there to benefit from her services. A statement such as ''I miss you'' implies SHE is losing out by your absence. And imo that is unprofessional and unethical.
If I miss an appointment or more, and my t calls me to check in, I expect something along the lines of, ''i'm concerned about you. Would you like to talk about what's going on for you? If I can be of any help don't hesitate to call me''.