The direct counter to enshittification is interoperability: the ability to pack up your content (likes, followers, messages, uploads) and import it into another service provider.

Since Signal is open source and mostly FOSS, you can theoretically create a Signal fork that can import Signal backups. I know because this program can read such backups and convert them into other formats. Ideally, the Atlantic reporter could have exported a Signal backup with the offending group chat messages before they expired.