Currently, I send all my troops at an island. They all die. Ship comes home empty, but somehow loaded with gold and grog. Did not see them carrying loot to the ship in batches before they died. Or I send a subset of my troops in after loot. I don't care that they die. As soon as I have my fill I "surrender". I think "Surrender" should mean coming home empty-handed. No loot. All deployed pirates lost. To compensate for this, I would suggest adding a "Retreat" button. When you press it, the pirates begin evacuating the island. Assuming at least one of them makes it, you come home with whatever loot has been plundered. If the last one is killed before he can get away, all loot is lost. Any pirates that do make it are recovered and available for the next attack. This will make it more challenging to 3-star as sometimes you'll have to ask yourself if it's worth the risk to continue letting an attack continue, versus retreating with loot before that.
Well I didn't notice there was another retreat thread but this is a different concept and involves changing what "surrender" does. Really "retreat" would become the norm for grabbing some quick loot from a base too powerful to defeat.
