I'm going to second this. There have been times (particularly for my FA work) where I have had to admit that I cannot do what I used to do. And, despite my guilt and the fact that it took at least three people to replace me - life has still gone on. My guilt has lessened over time. I also agree in that if you make yourself unavailable, people will FIND a way to get the job done. It is not your job to keep the world from falling apart. You contribute what you can, and let others do their share for the rest.