When the hard drives appear offline it means that the RAID could be corrupted but it does not mean that the hard drives are bad.
You can access the RAID BIOS in your motherboard and set only that hard drive to non RAID disk; that will delete the RAID structure from that hard drive, then in Windows from the Intel Matrix Storage Manager software you can rebuild the RAID 5 volume using that Hard Drive again.
I had one drive fail. I could hear it spinning down and attempting to spin up. I replaced it. When I rebooted, the BIOS prompted to add the new drive (or something like that). When I got into Windows the storage manager didn't load and I had errors so I rebooted. This time the BIOS showed the other two drives as offline members. I don't think I remove them. It seems like they have been erroneously marked as offline. I'm looking for some way to mark them as online again so that the storage manager software can re-build the array.
You might want to re-post this query in the Chipsets support forum. There are experts monitoring that forum that can better handle issues related to Intel RST.
P.S. I would move it over for you if I could figure out how it is done...