The first one took off about 2 months at a time a couple of times. She did not volunteer what she was doing and I did not care enough to ask. I took breaks from appointments with her and she took time off as well. It really did not bother me. The second one took off a few weeks every year as did I. Again - not a huge deal to me one way or the other.
If I thought a therapist was away so much that I found it not useful for me, I would find a different one. I am more surprised when one of those guys takes off months at a time because of how they seem to sell the idea that they are more needed than that usually.
I was always mildly insulted/thought it a bit overly self important when the woman would tell me a month in advance that she was going to be gone for a week. She was not such a big deal to me that the idea of her being away was going to cause me any concern.