I will assume that your question pertains to the United States. In other jurisdictions, different rules could apply.
The usual penalty for spoliation of evidence (the technical term for what you describe) in a civil case is a judicial determination or jury instruction that the evidence destroyed would have established the relevant part of the other side's case had it not been destroyed. In all of these cases, your failure to take affirmative action to preserve the evidence once you knew that there was a bona fide likelihood that you would be sued could be held against you by making an adverse determination that the evidence would have been unfavorable to you and possibly also money sanctions. You could not be held in contempt of court for this if these events happened before a case was commenced.
In a criminal case, where you are a defendant, you have an absolute right to not incriminate yourself and do not have to take affirmative action to preserve evidence, although this right is limited to criminal cases and your failure to preserve evidence can still be held against you in a civil case.
Certainly, in situation 4 you are a potential criminal defendant, so the 5th Amendment protection would apply.
In situations 1 and 2, where the precautions were not put in place to facilitate a crime, the 5th Amendment would protect you if you were a potential criminal defendant, but suppose that you are a bystander like a third party ISP representative. If you were a third party, at a minimum you would have to be put on notice of the police need for the evidence, would probably have had to have had the police ask you for the evidence, and of course, would have to be aware that the destruction was imminent and have the power to prevent that destruction. If all those conditions were present, you might be guilty of obstruction of justice (there are precedents for inaction knowing of the consequences in the fact of a police question amounting to obstruction of justice).
In situation 3, this kind of action pretty much amounts to being an accessory to some crime before the fact (unless someone was successfully deceived by a very elaborate story) and would likely make anyone involved part of a conspiracy to commit the crime that the destruction of the papers would facilitate. While the papers themselves might have been evidence of a crime or civil wrong, the destruction of the papers might itself be considered part of the crime, regardless of what could be established regarding the actual content of the papers.