Agreed. Normally with RSRD or TMO or RFB your mission won't be fruitless and the mission directions will give you a radius you must stay within from the patrol center point and the amount of time you must remain there. Rarely, you will get a "sink tonnage" instruction. In that case, you can leave your patrol area to do that and still get credit for completing the mission!
With the stock game you may be just stuck with abandoning this mission. But sinking ships is the path to forgiveness. Don't come back empty and it won't hurt your career.
So go promote the ecology by creating some fresh, new fish habitat!
