Can FFCs be performed entirely in post-processing or off-line without data loss?

This answer applies to Tau2 and Quark2 cameras: An FFC can be applied in post processing, but doing so does not eliminate the need for a shutter – or some other uniform reference source – to optimize the image quality. Each pixel requires a unique offset at any given time. Even when the sensor is stabilized at a given temperature, the required offset table at one point in time will not be perfect some number of minutes or hours later – there is some unpredictable drift or 1/f noise. It is possible to store offset correction tables for several temperatures and apply them after the fact with reasonable results, but not with optimal image quality.