Fortunately, the first part of the first sentence is incorrect as of April 2, 2013. I (playing Dutch on Immortal) had all my Buddhist cities converted to Islam by Egypt (they've been spawning prophets and missionaries like crazy the whole game), and they also converted enough surrounding cities (+42 Islam pressure) to overcome my Holy City +30 Buddhist pressure. I thought I would never gain my own full enhanced religion (I had Tithe, Mosques, and Pagodas chosen) back.
Then I noticed this discussion, and once I reached Industrial Era, decided to try purchasing a Great Prophet in a city following Islam. Low and behold, the Great Prophet was tagged as Dutch, so I was able to use it to convert my three cities back to Buddhism.
Having learned my lesson, I also purchased an Inquisitor right away in one of the cities I converted, and stationed it outside my Holy City.