First I will give my experience. I spent over 12 years with the Foundation in San Francisco. At some point, I felt I needed to give attention to other things, especially after a death in the family. I left. Nobody coerced me to stay or tried to pressure me other than a few folks saying they would miss me. I spent a few years away, moved to a new state and eventually made contact with a much smaller group in my new state. Gurdjieff groups simply do not have the means to coerce people like a big organization has. Most of the groups are being run by people who make no money from their involvement.
That said, I could understand that some groups could become abusive. Gurdjieff left a somewhat open-source philosophy, meaning one could approach it in very different ways. Gurdjieff wanted people to ask questions, to think for themselves and to not follow things they did not understand. Thus there is not a set of rules that he left to dictate how a group should be run. Anyone could effectively start a “Gurdjieff” group and some of those who have started groups were not qualified. Like any human organization, there can be some pretentiousness and/or rigidity that creeps in. However, if you are having problems leaving, that in itself may be the best reason to leave. If you even have to ask the question about how to leave then you need help and need to get away. Ask someone in your local area for help. If you don’t have anyone to talk to in your local area, you might consider what is holding you there.