What to do if sshfs / fuse freezes your system?

Two things you can do. If it's generic fuse:

fusermount -u -z (mountpoint, don't tab to get the directory, you have to enter it exactly.)

If it's sshfs, you can reduce the timeout to have your system return from the ice age sooner and automatically next time:

echo ServerAliveInterval 15 >> ~/.ssh/config

And don't bother, this bug is know and has been reported before.