Ouch! I once learned that lesson myself many years ago, though not with astro images.
I keep my raw images in two places at once, until processed - camera card or laptop (depending on capture mode) and special astro HDD. Then I keep the finished products on my main HDD which is regularly backed up to another. I never give Mr Murphy a chance - he's a right b*stard.
Hope you figure out a way to recover your data.
Did the drive simply not spin up? You could try gently tapping it at boot time - it could work, even if it's unlikely - I saw it work once.