If my CAIR panels deflate in my AP saddle...if they died within 5 years, I'd tell Bates to replace them. After that, I'd probably just ride and see if my horses noticed a difference. I would be surprised if they did, but I ride with a Navajo blanket so I'm not exactly the typical English rider!
Mine fits Mia, but rides a little low in the front on Trooper. Today I took one of the Wintec white foam pads, cut it in half in the middle, and used the front half. Trooper seemed very happy with it (he seemed to enjoy trotting and remained happy when I rolled back a bit on my seat pockets while sitting the trot), and afterward there was no sign of a line where the foam ended. I don't ride my horses competitively or hard, so I suspect they could go for years without noticing a deflated CAIR panel. For myself, I wouldn't miss the extra bounce it seems to give.
In fact...anyone got a needle?