You can select the remaining 80 GB hard drive that was part of the RAID 1 and set it as a non RAID hard drive through the Intel(R) Matrix Storage Manager or Intel(R) Rapid Storage Technology Control I option ROM and since this is a RAID 1 or mirror, the data will remain intact on it.
This information is explained on the following article:
I suggest you to check on this, and verify if the configuration that you used complies with what is state there. If so, you can proceed and remove the RAID 1.
As a heads up, the control I option ROM may warn you that the data will be lost, even though it is not, this happens since this is a generic message that will be shown every time that the delete or reset options are selected, this does not change depending on the RAID type used, so it may not apply in all contexts.