I'm not sure if you want comments or, if you do, what kind of comments are appropriate to your therapy (it does seem different enough where you live that I don't want to be totally off base).

I went through this when my therapist was on a very tiny vacation a couple months ago, and decided to just say what I felt, which was that I was really glad she was back. I don't know if you're glad that your therapist is back in the same way that I was glad, but another option could be to tell him whatever it is that you think or feel about his absence and return.