I've known people who have left groups not as intensely controlling as this, but very controlling. There is typically a very long period where they aren't directly controlled by the group, but are very much still "engaged" in the sense that their interests still intersect quite a bit with the group. (Wanting to spread warnings, rescue people they know, etc.)

I'm sure there's a psychological model for this, but I think that's why there's so many "ex-XYZ" groups. Leaving is both abrupt and lengthy. Especially so, I imagine, for a group so totally psychologically consuming.