I think the site's broken at the moment, I can only see the word "oak" and nothing else when I click on it.
But let me speculate on what would need to happen to "defeat deafness". Keep in mind I'm only putting this up for the sake of debate and playing the Devil's Advocate.
1. Medical Technology has to advance way ahead to the point where the ability of the brain to receive electro-chemical signals can be restored. This could mean repairing the cochlea, or the neurons connecting the inner ear to the brain, or the tiny hairs on the middle ear that carry the sound waves or whatever else I'm missing. This is a major step, since without repairs to the hardware (or rather, "wetware"), there's no point in trying to repair the "software", except as a matter of improving upon what's already there.
2. Speech Pathology and Neurology needs to advance to the point where you can basically train the brain's speech/language center so that the recipient can make out words/tones/sounds like any hearing person can. This with step 1 would cover any existing deaf/HoH folks.
3. Virology and DNA/Gene Therapy needs to advance to the point where it can identify/stop issues that causes problems for hearing development during the fetal stage. In addition this would apply for diseases/trauma that affect the ear/brain and in turn affects hearing, such as spinal meningitis, very loud music, loud explosion sound destroying the eardrum/ear, etc. There is already limited gene therapy technology for other genetic issues. It's only a matter of time until one is found for repairing hearing development.
When all 3 are in place, then that would probably be the point at which the deaf population starts to diminish. There would of course still be people that choose to remain deaf whether it's a cultural choice, or financial or personal. That would last about 1 to 2 generations before it's gone.