PFS would not help in this case. The FBI asserted that a pen register (which is not a warrant and merely requires the government to assert "relevance") is sufficient to obtain the SSL keys for an entire service, because they choose to implement it via an SSL interceptor. LavaBit argued the pen register does not grant such broad power, so then they went and got a search warrant for it instead.
Obviously if the FBI has the SSL key, they can impersonate LavaBit and intercept everything at that point. It helps only to prevent the NSA reading their old packet logs.
The news here is not change your crypto - it doesn't work in the face of the $5 wrench attack (more accurately, $1000 fine per day). The news is that the FBI believes (and the court agreed) that the only thing they have to do to obtain an SSL key is assert that it is "relevant" to an ongoing investigation, an extremely low standard that is almost meaningless.