Exit tmux window without quitting the Terminal program

The reason why an event-script fails to send a "growler" message is that mcabber closes the standard input, output and error streams when it runs an event command. You can see this in hooks.c:

  if ((pid=fork()) == -1) {
    scr_LogPrint(LPRINT_LOGNORM, "Fork error, cannot launch external command.");
    g_free(datafname);
    return;   
  }    
  if (pid == 0) { // child
    // Close standard file descriptors
    close(STDIN_FILENO);
    close(STDOUT_FILENO);
    close(STDERR_FILENO);
    if (execl(extcmd, extcmd, arg_type, arg_info, bjid, arg_data,
              (char *)NULL) == -1) {
      // scr_LogPrint(LPRINT_LOGNORM, "Cannot execute external command.");
      exit(1);
    }
  }
  g_free(datafname);

That makes the event script run without interfering with the streams used by mcabber.

There is no special ncurses mode intercepting the message (after all, tmux is already running as a terminfo application). You can probably work around the problem by redirecting your echo (preferably printf) to /dev/tty, e.g.,

#!/bin/sh
printf '\033Ptmux;\033\033]9;foobar\007\033\\' >/dev/tty

From the tmux FAQ:

******************************************************************************
* PLEASE NOTE: most display problems are due to incorrect TERM! Before       *
* reporting problems make SURE that TERM settings are correct inside and     *
* outside tmux.                                                              *
*                                                                            *
* Inside tmux TERM must be "screen" or similar (such as "screen-256color").  *
* Don't bother reporting problems where it isn't!                            *
*                                                                            *
* Outside, it must match your terminal: particularly, use "rxvt" for rxvt    *
* and derivatives.                                                           *
******************************************************************************

http://tmux.git.sourceforge.net/git/gitweb.cgi?p=tmux/tmux;a=blob;f=FAQ