Success means the process ran with no errors. If the process ran and the logic in it didn't provide any features to the writer(s) and didnt cause any errors, then the process ran successfully.

A transformer to look at would be the nofeaturestester. Place this right before your writer(s). There are two output ports, one for features that enter in input port and one that will output a single feature if no features enter the input port.

You'd use the second port to hook into a terminator which will cause your process to fail if no features reach the writer(s)