At the moment (ArcGIS GeoEvent Extension 10.3.1) the rollback option is not exposed to the user and set to true on the 'Add a Feature' or 'Update a Feature' output connectors. When a transaction tries to add/update 100 features and 1 is giving an error, 100 features are lost.
Exposing the rollback option to the user may reduce the amount of data lost.
