just an idea
remove the new disk
go into raid bios and set the last disk that failed to good and try booting. (sometimes it works but not always)
if that works try rebuilding again with new disk
ofcourse this requires downtime. but you will need downtime anyway as i been reading.
Since your vm's running on a NFS datastore you should be fine to reinstalling on other disks/usb or other server and add the NFS datastore to the new server