Last tested: Mar 1, 2018
The quick answer is no! A user with the dashboard open in a tab will be able to access that dashboard until they do a browser refresh, or navigate away from that page. At that point they will see the "Dashboard you requested could not be found" screen.
Note: While the tab/live session is active, the user will be able to Clear Cache & Refresh the dashboard with no problems. An Admin may need to disable then reenable users in order to ensure that users can no longer see the dashboard.