My previous T went away on vacation all the time, at least 16 weeks out of the year, which I think is totally excessive. I have been seeing current T for 8 months and in that time she has been away for 2 weeks. She is diligent about being predictable and giving plenty of advance warning so I don't expect her to be away within the next few months either (unless she is ill, of course).
I very much prefer the predictability of T2. Although T1 was a very committed T when she was present she was simply not-present too much for my liking.