The Catholic Church itself have never determined the percentage of gay priests. Outside groups have tried to determine it. The lowest percentage ever estimated is 15%. Other estimates are much higher. Of course, no one knows.
In reality, no one should care. If priests are performing their work as required, what difference does it make whether one is gay or straight? Those defending the Catholic church often blame homosexuals for the child abuse problems. There is not a science based rational for that. I'm sure Catholic research universities would not endorse that view.
From everything I read these days, there are not enough priests in the pipeline to replace the huge number approaching retirement. Some perishes do not have priests today because there are not enough of them.
So, if the denomination went on a witch hunt to ferret out all gay priests, and the number was about fifteen percent, it seems it would make staffing problems even worse. There have to be some gay student priests so they would be gone as well.
From all of this, we can see what will become of gay priests. Nothing. There will be no purge. They will continue to serve and those in seminary will become priests.