In Content Translation, a warning is shown when the source article you are translating was changed.
The warning indicates that the translation can be restarted with the new content but does not indicate how to do so.
We can provide an action to restart the translation, but we need to clearly communicate that translated contents will be lost.
I think allowing the deletion of a published translation should be the first step towards achieving this. Published translations are definitely saved somewhere outside CT.
This is covered already in T168287: CX2: Warning about article having changed too much, the pending parts about the restoring process will be covered in T220790: Restore using updated content only when no user data is lost, using the original version as a fallback.