The nightmare of a pet service? When a dog walker or pet sitter calls out sick shot notice!

I can't think of anything more stressful than when a walker or pet sitter gets sick short-notice and can't work. Sure I have emergency plans in place, backup walkers, help, etc. but it's still so consuming:

* I have to alert all the clients on the route that they will have a backup walker and we might need to cut time

* You need to get all the proper dog notes to the backup walker(s) (I use Google Doc's for this)

* You need to get the keys to the backup walker(s) and they should already be labeled with the proper dog's names (though sometimes they will not be)

* All the while you need to keep running your company too.

And this all sounds orderly enough but what if you don't have a backup that day (I'll need to have active walkers eat up the walks and/or cut time on walks to do so and will have to alert all dogs to this, though crated and/or sick dog can't be cut)? And what if some keys aren't properly labeled? And what if the dog notes are not up to date? You can have a lot of chaos on your hands. Days like this are the reason I'm so strong with my walkers about updating their dog notes, labeling their keys and being in touch with me about how they feel. If they even feel a little sick I want to know then, not when they can barely stand. I've also taken an initiative to keeping my walkers healthy with their nutrition, the clothes and shoes they wear.

What have your experiences been? And what are ways you have come up with to combat this issue? Thanks!