The output will be reduced. If the drum is centered in the stereo image, the subwoofer will not have an output, as the drives to the voice coil will cancel.
Now when clipping happens they say that it will damage the speaker since the speaker coil will be stationary and current would flow and the coil will get heated.
Doesn't the same type of thing happen in this case?
Clipping allows DC to flow in the coils, leading to increased heating. The coil is not actually stationary in the sense of remaining in the undeflected position, but may be deflected in one direction as far as the structure will allow it to move.
Heating in the case of reversed polarity in the voice coils will be a function of the currents in each, not the degree of deflection.