"In hindsight, would a cheaper backup system (i5 workstation with a single external USB hard drive which gets swapped out with other externals as the week progresses) have been more sufficient than a bells-and-whistles backup system that tend to bork horribly just by looking at it the wrong way?"
The thing is, the only reason they would be attempting to recover data from the borked RAID array is if they were treating it as their backup system (repeat it with me: "RAID is not NOT backup - never treat it as such") and don't have a regular backup regimen to tape or other media.
My understanding is that the system failed during a critical upgrade. It seems unlikely that a mirrored array would have both drives just die - it seems more likely that that someone failed to replace an already degraded drive, and then casually kicked off the upgrade with only one drive in the mirror working.
If so, a classic example of accidents tending to be the culmination of a series of errors, rather than one isolated issue.