Exactly. There's no reason for the government not to torture all suspects to death, because they can never be sure that there's not another volume somewhere, or whether the outer or adjacent volumes that they've gotten access to that appear to have the information that they want are decoys, or even whether the bearer of the computer has knowledge of or the ability to open the relevant volume which may or may not exist or be a decoy.

The rational thing for the government to do would be to ignore the computer (after forensics), and work on the person. If the information turns out not to be productive, escalate the torture. When the suspect dies and/or fools you into a significant expenditure or public failure, you lose and the suspect wins. Same as it's always been.

edit: of course, faced with the fact that there's no reason not to torture you to death, you may just become a willing collaborator.