If the all the monsters somehow got out of the underground, would the hunger and mutations recede? Would they continue to get worse, or would the hunger just be a scar they would live with for the rest of their lives. Also how many monsters are left in the underground.
If the monsters escaped the Underground, and the barrier remained in place to keep the disease trapped there, their Hunger would fade and the mutations would halt… but not reverse. Their disfigurement, and mental trauma, is permanent. Some could recover their faculties in time, but few would be able to live with the things they did. Any that didn’t fall from their own self-disgust would dust themselves.
As for how many monsters are left… probably less than 2% of the population, at this point. Around… 100,000 of the 5.5 million there were.