People already assume their voice conversations are (usually) ephemeral. As long as it is explained properly, an ephemeral text chat can not only be acceptable,

People already assume their voice conversations are (usually) ephemeral. As long as it is explained properly, an ephemeral text chat can not only be acceptable, it may also be a feature. More importantly, why are you pretending that end-to-end encryption implies an irretrievable loss of data? If desired, backups can be made locally or to another local device such some type of LAN-only network storage or a USB storage device.