Redis is not an ephemeral database when used in Twilio's configuration. When configured with an AOF with fsync set to 'always', Redis will be as durable if not more durable than postgres and the like.
Redis has a reputation as an "ephemeral database", because it's usually used as one, but there's nothing inherently ephemeral about it. This isn't magic; it's just file I/O.
guessing by your username where you may be from, you may be aware that freshness... err... durability comes in only one grade - first grade :)