Error on Raid (0) - Imidiate backup?

You'll need to make an image - Acronis True Image will do the job nicely - to an external drive, and then restore the image once you've replaced the faulty drive.

I'm guessing I have to rebuild the raid.   Can I do this without risking losing my Recovery Partition?

Assuming you can't just get away with running the diagnostics tests, and fixing any bad sectors on the hard drive(s), you'll obviously need to replace the duff drive with another similar drive.

You can then setup the RAID array in the BIOS.

It's very easy to do, but one of the longer standing forum members has a number of videos on YouTube, in which he describes how to do various things with a M1730 specifically (replace hardware etc)... but I suspect the procedure is pretty much exactly the same for any laptop? 

Anyways... one of the videos describes how to replace the hard drive(s), and then setup RAID 0.

This is the video in question, but if you're happy enough in swapping out the hard drives yourself, fast-forward the video to around 4min 20secs (roughly half-way), for the part where he describes how to setup RAID 0 specifically.

Note:   Thankfully... no RAID drivers are required!  It's all done in the BIOS, just by selecting/changing a few different options :emotion-11:

How to I restore it to dell's default settings again afterwards?

As long as you've still got the recovery partition, you can restore the system from the OS disc.

But see here for the official Dell 'how to' :emotion-5: