I just switched to TeamViewer9 since LogMeIn Free will be gone very soon.
I do not get the TeamViewer window open after disconnecting (might be due to an automatically minimize TeamViewer option in advanced settings), however I was getting the stupid nag prompt.
This is the script I use:
Change sleep to your preference. It works great on an "old" win7 x64 AMD laptop I tested it on, mostly using 0% CPU and sometimes flickers 1%.
I also added it to start automatically under HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindowsCurrentVersionRun