Protalix management should've spoken to Merck not Pfizer about a takeover. $2 billion is nothing if it gives Merck a way around their competitions method based (Chinese Hamster Ovary cells) manufacturing patents.
Orphan drug makers seem to be in demand to be acquired. Many potential big pharma with orphan drug programs could be interested. Protalix should explore all options. Other than Pfizer, I could see other companies such as Sanofi (Genzyme), Shire, Biomarin and Bristol Meyers being interested. The platform itself would make other companies take a look.
If Protalix chooses to remain independent, I think it is because they see big future potential.
Does the stock price really reflect the possibilities? I don't think so.