Lost all my data on my RN104 - anything I can do?

Just to be clear. My email alerts were indeed set up but I didn't receive any alerts. It is possible that there was a glitch in the email system.
The first time that I was given any indication that anything abnormal was occurring was when I got a yellow warning notice at the top of the admin web page telling me about a problem with disk 2, the Seagate, I never received any warning about the other failing disk EVER!!! The yellow notice showed up after I updated the firmware.
My comments about casually glancing at the logs still stands. As of right now with the bad Hitachi drive in the box my admin page reports the status as "healthy". So I did indeed run with bad drives for a number of months without every knowing about the problems until it was too late. And yes the error counts are huge, so why didn't that trigger the software? The status says healthy but the logs say something very different. I'd say that was a problem.

So that's my experience so far with this Netgear box. Am I disappointed? Somewhat.. I don't expect a perfect system and I have had many years of hard drives, tapes, SSD's, and discs failing so I realize that there isn't anything out there yet that's going to be perfect. I get that it's not a matter of if but when and when this Nas failed it didn't totally shock me but I did hope for something a bit better than what was delivered.

It's up to the user to interpret the warnings we give. We won't ever mark a disk as failed simply because it is throwing some errors. It has to get to the point where e.g. it fails a self assessment test or badly fail to respond for it to be marked as failed.

These are clear warnings that you would have seen in the UI if you looked and if you had verified email alerts were working you would have got email alerts about these. There would have been alerts in the UI about disk problems over several months whether or not those alerts showed up as yellow or not.

Furthermore no important data should ever be stored on the one device. Always backup your data. There are other problems that can happen such as fire, flood, theft etc.