Maybe Audyssey will EQ down to the minus three dB point in room and pass that point along to the receiver to allow the receiver's logic to choose a crossover. Presumably, in that case, the receiver would use it's highest crossover, somewhere like 200 Hz, and there'd be a multiple octave hole in the sound.
Alternatively, Audyssey MIGHT include logic that would tell it that a speaker with no response in the woofer frequency range is defective. Then it would report the speaker is defective and refuse to proceed (I think).
If a person happened to have speakers that can be biwired/biamped, he could experiment by removing the jumpers and attempting a calibration with only the tweeter of one or more speakers active. That should tell you what Audyssey would do . . .