SHIT happens - let's hope you weren't the ONLY seeder on those...
Sadly, for you to recover those files, you will have to re-download their torrents - which will hurt your download rights. With luck, that's not a problem for you.
Just something to think about in the future: RAID
I use a device from QNAP, many others use devices from other companies (Syology is also popular)... it's worth the investment so that when your hard drive fails (they ALL fail eventually, folks!) you don't lose data!