There are two things that can go wrong.
1, it simply won't work which means, Usually, you put the BIN file in the wrong place on the card or it's the wrong file. As long as the file is in the root directory of the card (you'll be looking at the BIN file as well as (possibly) the DCIM directory) and is the proper file, shouldn't be any problems.
2, The firmware update will fail due to camera shutdown during the process. In this case, you have a pretty (insert color here) brick. This will require a trip to Pentax Service (Arizona) to correct, at your expense.
There is a third possibility but it is rare and that is the camera will simply hang up during the process. This will force you to shut it down and may or may not have the problem described in 2. In this case, pentax may repair it at no cost. It Has happened to others here before.
The part of the instructions I urge you to follow to the letter is to make sure the batteries are fully charged (or fresh batteries).
No, I would not send the camera to Japan for an update of firmware. It'll cost you easily $50+, plus the service call, and you'll be without your camera for a month or more.
When you start the update, you will see 3 things happen. A progress bar will show on the rear screen that says Phase 1/2. Leave the camera alone at this point and just let it do it's thing. After about 60 or so seconds, you'll see Phase 2/2. This will take longer than phase 1 but Still, Do Not Touch The Camera. 90-120 seconds after Phase 2 starts, the update should be finished. The screen will show Completed and the Red card access light (near the card slot) will blink. Turn the camera off at this point, your firmware has successfully installed. Now remove the bin file from the card as it is no longer needed.