Question

what will happen if the eardrum is absent from our ears?

Answer 1

Eardrum is the organ that is responsible to convert the vibrations of molecules in the air(sound) and pass these vibrations to underlying ossicles.
Ear drum acts as a satellite.
If the ear drum was absent, there would be no functionality of ear ossicles and cochlea. 
Although, semi-circular canals and the cochlear fluid would be still functional providing dynamic and static equilibrium to the body respectively, only the sensation of hearing would be lost.

Answer 2

eardum is a part of a hearing organ.a thin and steched membrame is called eardrum.so it is necessary to hear the sound.