It does, however, mean that your new documents related to the litigation must be preserved. Just because a machine destroys it for you as a service doesn't mean you don't have a duty to preserve. They control the disappearing time.
Looking at FRCP rule 37, it uses language like "reasonable steps to preserve" electronic information, and "intent to deprive another party of the information’s use". I'm no expert, but it does sound like this might imply an obligation to change retention settings, switch to another chat app, or figure out some other way to preserve relevant information (if litigation is anticipated).
