Users can continue to generate output from a published Form that is being edited so long as the edited Form has not been published.
However, once you publish the edited Form you can no longer generate output from the older version.
When you edit a Form you might want to keep an older version. You can clone the Form before editing it and give it a new name (for example: FormX _VERSION1). To use the cloned Form you need to publish the Form.
To learn more about Form statuses refer to Form Lifecycle.
To learn more about creating a new version refer to Updating a Form – Form New Version