NoSQL doesn't mean NoDurability. Many of them offer better multi-datacenter durability and availability by dropping ACID for BASE. I suspect that most data by volume belongs in a BASE database. Some of them also support a mixture of immediate and eventual consistency in the same database.
Durability is a generic topic, not only the problem of NoSQL.
Some of the NoSQL solutions take durability very seriously, some put it second to looking good in benchmarks. NoSQL is about choice, and the most durable of the NoSQL stores are more durable than many of the venerable relational databases.
For instances, what CouchDB treated as a major bug, is the accepted behavior of many relational databases. (Eg, data isn't lost, but must be recovered via a long-running process should there be an uncontrolled shtudown.)
Riak and Cassandra also have modes that treat durability as paramount, and give you better assurances than MySQL or even commercial RDBMS products.
If you want a lot of speed and can tolerate the possible (even if unlikely) data loss, use NoSQL.
If your business requires that your data is guaranteed and always up-to-date at any moment, then use RDBMS.