If the password is changed while the Planck Cruncher is doing its thing, and it changes to something that the PC has already guessed and tested negative, the PC is screwed.
Hint: Change your password regularly.
No.
In the real world having an actual high quality lengthty password is enough to deter anyone who is trying random accounts to move on for easier targets and anything that someone has physical access to, like law enforcement who confiscated something, will have an easier time bypassing the username and password process.
Changing passwords frequently leads to easier to break passwords, especially when you follow the practice of using a different one for different systems.
At that point go with a ridiculously long password to further decrease the odds of a lucky guess.