I’ve experimented a little with autosaves in SU Free. When opening SketchUp Free after it has closed unexpectedly, e.g. when the browser has crashed, you are asked whether you want to open the more up to date autosave instead of the saved file itself. So far everything is good.
However, if you chose top open the autosave it is immediately written onto the saved file. Overwriting a file without the users consent is unacceptable as it risks losing data. For instance if the user had cut out a part of the model to the clipboard but not yet had pasted it back into the model once the autosave was made, and the clipboard has been cleared since, there is no way to get back that data.
When opening an autosave the model must remain unsaved until the user manually saves it, giving the user access to the last manually saved file.