Having dealt with hotels recently for a wedding, I know that most I spoke with had a policy that if they could resell the date you booked, you could get your deposit back - some returned it all, others returned it less a minimal 'handling' fee (around €100 in most cases)
It might be worth checking out. I know on weddingsonline.ie and confetti.ie forums people have 'advertised' their date and hotel as available to let people know and hopefully increase the chances of getting their deposit back.
HTH.