Currently if you edit a survey while it is active it's possible to lose responses that have been completed - this just happened to me on a survey.
This is a very serious bug that needs to be fixed as losing response data is unacceptable. Other survey platforms allow at least minor editing of questions while a survey is live without incident. I'm not talking about rearranging questions or anything like that, just editing text or adding/removing response options. This should be feasible.
Alternately, if the above is not possible in the near future, the ability to edit the survey while it is active should be removed, or at minimum, a warning should be displayed that data could be lost.