Typically biotechs are valued at about 5 times sales - so that means Dyax worth about $250m just on Kalbitor -if sales grow, it's worth more.
But it's not best in class - Viropharma's drug is probably better because it prevents attacks - you can see this in how much bigger its sales are.
IP is certainly worth something.
My guess is someone big is trying to get out - since stock is illiquid, that pushes price below where it should be. So it's probably a good time to buy stock if you can hang on for a while - it could still drop more before recovering.