You shouldn't fear it. In the last years many MMOs have been forced to change their market plan to avoid bankrupt. There 2 main reasons to change from P2P to F2P:
1) An old game that is losing players, and want to keep them up as long as possible.
2) A failed game.
This is the most valuable proof about what I'm saying. I don't want to talk about P2P vs F2P, but if players pay a monthly fee and the game is full of people, there won't any reasons to change and go F2P.