P2P games would probably deteriorate if they became f2p. I know it sucks if you want to play a certain game but cannot afford it.
I played f2p MMOs for years before I started FFXI. I can honestly state that after playing a p2p MMO for such a long time I do not intend to try f2p games again. Community is usually SO much better in a p2p game, regular updates, better balancing.
P2P games have also actually saved me money as I always tended to buy cash shop items. So the monthly fee I pay is actually way less than I used to spend in f2p games.