I asked Posi in person about the PvP population at PAX 2011. That was right before issue 21.
He said it was 1% right then. That would have been the lowest it had ever been (It's not like anyone was joining PvP). If it was 1% -after- issue 13, then at issue 12, it had to have been much higher.
The population was small if you only count the people who only PvPed. Like I said, even a lot of people on these forums would have enjoyed PvP at one time or another (Casually, with friends, base raids etc.). In fact, you couldn't even PvP decently until you had logged enough PvE hours to get to level 50.
Those kinds of people didn't leave because of the i13 PvP, they just stopped playing PvP. You can't see the shift in revenue because they didn't lose money. It was just a huge quality of life fail. The lose of revenue would be seen over time as, until Incarnates, PvP was the only end-game for players.
Incarnate came out Q4 2010. The drops right after Champions came out was obviously caused by Champions, but I would confidently say a lot of people had no problem changing games because the lack of end-game (and lack of PvP). They were getting bored with their level 50s, PvP might have solved that for some of them.
Besides, I don't even know how anyone can measure the amount of people with PvP. What qualifies someone who PvPs? If they spend a certain amount of time in a zone? How many events they do in a week? I had a group of RPers that never PvPed but loved watching me duel people. What about them? We've had people wander into PvP zones and have no idea what's going on. Why aren't players told about PvP and where the zones are, the zone levels etc. There's a generic contact standing there that just tells players to get ready to be attacked.
Not only that, let's talk about PvP's potential. If we had 10% with a neglected game type, imagine if they talked to the PvPers and spent some more time on it.
I think the PvP population was actually bigger, just like the base building community was bigger. I hated building bases, but I enjoyed looking at other SG's bases. It helped me stay with CoH and helped CoH get my money, while I couldn't build a base for the life of me. I wouldn't leave the game if bases were taken out though. Some people would, but a lot of others would think "That really sucks", then move back to PvE.
That's what happened with PvP. As for our real population numbers? I'd have to see their parameters for the data mining, and I doubt they were all inclusive.