Coincidentally, this question came up during an initial consultation with a prospect yesterday morrning. I never say we're the "same quality", I say we have comparable styles which is a very large distinction. We all approach the art in similar ways; enough so that if I had to send one of them in my place, the client would not be disappointed with the outcome.
And I do not talk about price to the client. I connected with photographers at a similar cost so that any one of us are comfortable covering for the other, passing any payments received, and everyone is left/made whole. But that's not discussed with the client; indeed, the very idea is to make it all seamless to the client; a replacement will show up and produce a high quality job and they will never have to think about the issue of cost.
And likewise, I have never had to send a replacement. A family emergency, a broken bone or sprained ankle, a very bad stomach flu, that may happen some day; but for a cold or some other less dramatic event, I'm taking pictures!