There are a few things that cannot be undone:
1) Once you click "Optimize" or "Re-optimize", it is not possible to force-stop the optimization process. Closing the web page will not stop the process, because the optimization will be running in the background and will still be completed for your project.
2) Likewise, once you dispatch a route, you cannot un-dispatch it. You simply have to re-dispatch the route with any updates you might have.
3) Once a driver has started a route, he or she cannot "unstart" it.