The idea that there is some contract here is ridiculous on its face. This place, indeed most of the internet is the 21st century version of the commons, when it comes to the discussion board aspect. The pre-internet analogy would be the demanding of the removal of all the things you said in the town square from everyone's memory. Bonnie Shaljean said it well. You don't own what you say here (excepting copyrighted material, properly notated) once you post it. It is "in the air".
As to Megan considering leaving, I am not sure what her motivation is but it is hers. The place would be lessened by her leaving though. I wish her well, and further wish she would stay.