If just one (or more) of the disks in a ccd fails, the entire file system will be lost unless you are mirroring the disks.
If one of the disks in a mirror is lost, you should still be able to back up your data. If a write error occurs, however, data read from that sector may be non-deterministic. It may return the data prior to the write or it may return the data that was written. When a write error occurs, you should recover and regenerate the data as soon as possible.
Changing the interleave or other parameters for a ccd disk usually destroys whatever data previously existed on that disk.