After extensive research I found that the one of the tile colors I would need to replace was no longer being manufactured and so I structured my bid to replace the whole piece with new tile that would coordinate with a tandem piece nearby. (There were 2 mosaic sections in this particular project and only one is damaged.)
A few days later I received word that the school would be removed and the space filled in with cement, so they would not need my services on this project. I'm not sure if that will mean the removal of the tandem piece as well, but it's not my call, nor my problem.
The deciding factor in their decision is funding. I guess this is the more economical path for the school to take.
At a certain point, many public art mosaics are slated for either repair or removal. It's interesting to me that I've been doing this long enough to have it happen. I'm working on being OK with the removal of some of my public art.