Well, there is no 100% foolproof method of breaking your Raid pairing and not losing data.
The only way to ensure you don't lose anything is to practice the "
Grandfather Principle" of Data Processing. That is, you need to make an external backup of your existing critical data onto an external device such as an external hard drive, flash drive, cd/dvd disc(s), or Cloud backup such as CloudDrive or GoogleDrive. Once you make that back--say onto a flash drive, you then need to make a
SECOND backup onto a different external media type; choose one of the others from the above list (external hdd, cd/dvd disc(s), or Cloud Backup).
This will be the best protection you can get approaching 100%.
If you really want to do it right, store the
SECOND backup offsite at a close friend's or relatives home in case you home gets hit by a natural disaster (flood-fire-earthquake) or loss of your computer via theft.
If you do all of this, and your "Raid-Breaking" bad (couldn't resist the pun there) fails, you have 2 chances to get your data back onto the boot drive. Of course the methods that bassfisher and I suggested to you says you can break the Raid pairing and reformat the 2nd drive in your Raid config and use that for one of your 3 backups! Of course, that may or may not work. As I worked for multiple companies that produced RAID drive systems I can tell you automatic backup upon RAID unpairing doesn't always work as there are a large number of variables that can cause you difficulties, not excluding Human Error.
You still won't be at 100%, but you'll be awfully darn close!
Good luck
and please make sure to let us know your result. Your Post could help someone else attempting to do this.
BIGBEARJEDI