I rarely take a vacation and if I do have to leave for a few days I let all my clients know when I'll be back. My daughter died and I went through breast cancer and radiation at the same time last year and I kept right on working so my clients aren't worried about my devotion or attention to their needs.
I am not a reseller host and all my clients own their own domain and I teach them how to manage it and pay for their hosting, etc., so if I'm gone for an extended time they can find another designer and move their domain if they have to. Therefore there is no need for my clients to be scared if I disappear for an extended amount of time other than the annoyance of finding another designer.
I've been looking for another designer but haven't found anyone that can both write code by hand and understands SEO (other than the gradeschool version of SEO). One of my grandsons is following in my footsteps but it will be a few years before he can take over, if needed.
I have written out brief instrutions for my family in case something happens to me but need to set it up in more detail like was mentioned above so thanks for the reminder.