If you are only giving demo you will have to unplug only data and power cables attached to disk. Dont remove disk phy.ly. So this will avoid damage to disk. Also post will report error on screen that disk is not available but still system will boot. After complete boot shutdown PC and reconnect disk with power cable and data cable. After you switch on system RAID card will detect disk and will start synchronization automatically. You will have to keep system as is for one day as sync. will take some time. System can be used during sync is in progress.
Next day repeat same test for disk which was not removed and system will work on second disk with same messages as of previous day. So follow same above steps for disk one as well.
If you do all these activity in front of customer honestly am sure they will consider your demo.