If you find yourself in this situation (and I hope you won’t!), you have some options to get your way with a misbehaving server remotely. You can force an immediate reboot with the following:
echo 1 > /proc/sys/kernel/sysrq echo b > /proc/sysrq-trigger
WHOA THERE! This is pretty much the same as pressing the reset button on the server (if equipped). No daemons will be shut down gracefully, no filesystem sync will occur, and you may get the wrath of a fsck (or worse, a non-booting server) upon reboot.