Thank you for reaching out to us. When a contract ends, clients usually leave you feedback as part of that process. As a freelancer, you also can leave public feedback about your experience with the client. We created the system to be double-blind, which means that feedback won’t be visible until both parties provide it for each other. We designed it this way to help ensure genuine, independent feedback from both parties. If only one party leaves feedback, we will post it after the 14-day period has expired. You can find more information on this page.
Yes, they do. I assume, but don't know, that Upwork notifies the client when you close a project and may then decide to leave feedback.
In my experience, most clients do not leave feedback when I close projects, which I usually only do due to inactivity and a month or more of no communication. I assume this majority have more or less abandoned their projects so they don't care and I never hear from them again. A few apologize for not closing their projects and leaving feedback. Maybe 10% or so come back later to re-start the project or to start a new project.
I always send a message via the project message board telling them a) they can re-start the project at any time and b) thanking the client for the work, even if a) is not true and I'd just have soon never have worked for them. Do what you can to leave the client in a good mood about working with you, but tell the truth in your feedback for the client so other freelancers will know what they're in for with difficult clients. Upwork won't tell us much about such clients; it's up to freelancers to tell one another.