I've never tried to "convert" a RAID1 into a singe HDD without a clean install - I'm thinking the easiest way to check is to change the controller from RAID to AHCI in the BIOS, and check to see that the system boots, but I've never tried that. I agree with Greg that a clean install is the fail-safe route.
I would try to plug in a 2nd HDD, and see if the RAID attempts to rebuild itself - it will take a long time. After that, try the image (what imaging tool did you use)? Does IRST show the array as per the screen capture image I attached?
Longer term, look to a clean install on a single HDD as recommended by Greg.