In Terminal, one can enter 'xkill' as a command which lets you select a window whose client you wish to kill.  In fact, it can even be used to kill panels.How can I restore an xkilled panel in Linux Mint without a reboot?Something that I generally do in Windows is Ctrl+Alt+Delete and then restart the explorer.exe service.
How can I restore an xkilled panel in Linux Mint without a reboot?
command line;linux mint
Pressing Alt+F2 and then enter cinnamon --replace might fix it.