I think they will have to. Under the Sale Of Goods Act(?) fans are not receiving the product they have paid for (watching live football, from your seat in a stadium) so a refund must surely have to be offered. That`s not to say fans shouldn`t have other options should they choose to take them up (free Robins TV subs, a `free` ST for the next full season etc.) but the option of a refund will have to be there by law I think.
One thing I hope the club don`t do though is penalise those ST holders that opt for the refund - they must IMO have the opportunity to retake their seat at existing ST prices in future seasons and not be treated as new ST holders.