A major edit to my original answer to capture the comments below.
The Friis equation, that I originally suggested, does not apply in this situation since the receiving antenna is only around one wavelength away from the transmitting antenna, meaning that it is still in the near field. At these low frequencies, also the conductive ground plays a major role. Accurate results can be obtained from simulations.
You can test the withstanding of your receiver by gradually moving closer and observing what happens. As the ferrite core antennas have somewhat high losses in the ferrite, the first sign might be that the antenna starts to heat up. On the other hand, if you are listening to the TX antenna, I think the first effect will be that the sound starts to clip when the output voltage from your pre-amplifier reaches the DC bias voltage.
My gut feeling is unchanged, I don't think the receiver will break down. Please let us know if I'm wrong.