No, most did leave at cata that I know, too. Cata ruined the playstyle of warlocks. Soulswap is a terrible ability, and in an ideal world would either not exist or be a very long cooldown. Also, RIP shadow embrace.
Everyone left at cata. It has nothing to do with warlock balance.
12m->9m subs in that expansion alone.
On topic: I'm still sticking with my destro prediction for next patch.
I get the feeling that Blizz doesn't want to give Aff what they want, and in the end the spread damage won't be significant enough to outweigh the better healing of destro (especially after damage reduction is taken out). Plus drain soul is looking to be even worse than live when compared to shadowburn with these nerfs.
Bye again! This game isn't fun when you don't know anyone else that still plays.