Obviously these are application decisions.
You, obviously, don't commit important data only to a session that you can loose, if the application does not allow it.
We use redis as infrastructure. To route events and as a cache.
For us redis could go down and we would merely see a degradation of our service with no data loss.
I recommend using redis like that. And then use a database that supports transactions for real data problems.
But we are different. And that's OK.
This discussion is a bit weird. We started off from, Redis should have better availability guarantees. Specifically to avoid the degradation of service you described.
But that requires running on multiple instances, which in turn requires to share the data across all replicas.