Store data from a specific content type in a different database?
This is not possible without a lot of custom code. Primarily because Drupal stores field content in separate database tables. There is not the one single table that holds the content of all nodes of a specific content type. And fields are also re-usable across different content types. You would need to create your own storage engine.

Wouldn't an intelligent backup strategy be enough to assure data security in your case?