I think you'd have to ask the specific therapist. It's possible for a therapist to be booked to the gills with people wanting to see him/her, I suppose, but I can't imagine it would be that common. Probably depends whether they work for an agency, or clinic, or own their own private practice, or whatever.

I've gone months without seeing my T. He's never suggested that I must keep coming regularly or lose the opportunity to see him at all.

Why not ask?

ETA: that said, my day/time changes if I take a break, and he's not usually able to see me the same week I call. I think if you are gone for a while, there's no guarantee that your time slot--the day/time you usually come--will still be available to you. The idea, though, that there'd be NO opening at all seems not too likely to me.