If a therapist is just out sick for a week with the flu or something, I wouldn't bother them with a text. If you had a huge urge to text about it, I would think it was more about having the connection than expressing get well wishes. Missing a session is hard, so I get that. But I personally would let the T recuperate in peace and save any expressions of concern for the next session. If the T was out for a long time with an illness, it would be different.