As I understand it, this will only remove liability for administrations of the drugs on or after 2027-06-29. The drug companies will not face liability for damages caused by their products (or “military countermeasures”) before that date. All current COVID-19 vaccine victims can hope for is compensation from the US federal government.
The drug companies will probably pull those drugs from the market before the EUA expires, but they are barely selling any of them now anyway. The relentless fear campaign ended a few years ago. People moved on.
Pfizer and Moderna’s stocks are not crashing in pre‐market trading. I doubt this will affect them.