mattyp, were you at The Band's Visit this past Tuesday (2 days ago)? I know Katrina Lenk had a scheduled week off at the end of January and also one in the fall. I had heard that her planned vacation in the fall was the first time she was out of the show at all.
I would be bummed if she was out as well. I don't know if shows are more demanding than they used to be, but in the past few years, I've noticed that the usual times when it's somewhat safe that the full cast will be there are not as true as they used to be (previews, the first couple of months after opening, Tony season).