Fading is caused by conditions in the D, E, & F layers of the ionosphere. These conditions can absolutely drop the level of a signal to undetectable levels. Nothing you do in a receiver can overcome the complete lack of a signal. Some relief is provided by an AGC (Automatic Gain Control)circuit, but these have a finite reaction time which does not allow smooth transitions between high gain and lower gain conditions.
There is also a limit to how sensitive you can make a receiver. There is a point caleed the noise floor where the signal has less energy than the noise cause by all the different sources including the cosmic background radiation. This level is about -176 dBm. There are methods for recoveing information burried in the noise floor, but they are for digital information, not audio..