I have lost total mouse and keyboard input after launch. Both work fine all the way through login, character selection etc, and just totally failed after launch. ALL keys and mouse operations failed. Have to force computer shutdown with power key!

Anything interesting in ~/.vendetta/errors.log?

If you want to test without having to power down any time this happens, open a terminal and run something like this just before you start the game:

sleep 300; killall vendetta; sleep 10; killall -9 vendetta

Basically it will wait for five minutes and then try to kill the game "gently". Then just in case that doesn't work, it waits another ten seconds and tries to kill the game more harshly.

Some things to try:

Alt+Enter - This is the game's hotkey to switch to windowed mode.
~ - Opens the game's console. From here you might be able to do /logoff or something.
Ctrl+Alt+F1,F2,F3,etc - Switch VT. This should get you to a command prompt login where you can try pkill vendetta or some other command like the ones Pizzasgood suggested.
Ctrl+Alt+Backspace - Xorg "zap" will kill the X server if it hasn't been disabled by your distro's default config. You'll probably have to log back in, but its faster than rebooting.

I'm having the same problem, keyboard and mouse stop working completely after entering game. Key commands won't work because keyboard doesn't work.

My only suggestion at this time is to delete ~/.vendetta/wgaf.cfg to have it recreated.