Cannot boot Mac Mini with striped RAID 0 set
When you use Apple software to stripe the two internal drives of a Mac Mini, the recovery hard disk is removed. That means you will need to boot from a next journal drive to run Disk Utility and figure out what happened to the volume structure.

Fast SDHC cards are getting so inexpensive that I pretty much make one of those for every Mac Mini so it has a recovery OS to boot from for maintenance like this. Of course a USB drive works well too. 

Get yourself a new drive and worst case, use internet recovery to install the OS on to an external drive so you have something to boot from. If you have a backup, you could wipe the two drives and run internet recovery as well to just fix or reinstall the OS on the empty drives.