Both Mimic Intro and Mimic Pro will prompt you to save any work that needs to be saved by displaying a save button. If you make changes and don't see a save button then the simulation automatically saves the work for you.
Usually, content that is typed will display a save button. For example, content that is written on the landing pages or in an email campaign. However, if the simulation doesn't prompt you to save any work after you make a change then it is automatically saved and you can exit out of the simulation without any worries of losing your work.