If the risk of keeping the system running while the array rebuilt was deemed to high, I would have just gone with a dd/ddrescue of the remaining disks onto new

If the risk of keeping the system running while the array rebuilt was deemed to high, I would have just gone with a dd/ddrescue of the remaining disks onto new disks and then moved on from there. +1 for mentioning ZFS. It's really quite amazing. Almost like futuristic alien technology compared to the other freely available file systems.