For 3 months? That's real long. Has she/he a good reason for it?
I'd be upset but it'd depend on his reasons. Like if my T decided he wanted to travel- I'd be angry at him. If the reason was medical- I'd be worried about him...
I went for 3 months without therapy- my decision, traveled through extended summer vacation. I didn't miss him (it was in the beginnings of my therapy) but it sure was a bit awkward for few sessions when I return.