They put the girl in a warehouse not too far from the next one, where Li Yifei retied the girl in the same manner as before. This was done so that when the girl woke up, she would still think she was in the original warehouse, thus not suspecting that there might be something off about that place.
As for the two kidnappers, leaving them in the sea would leave the police clueless as to who was behind it. As long as it didn't involve their current operation, Li Yifei didn't have to bother about it at all.
After completing all this, Li Yifei returned to the first warehouse and found what he was looking for. The item wasn't large; it could be packed in a backpack. It was a core piece of technology and, more importantly, it contained the data. Huaxia could handle everything else on their own.
By this time, Sophia had also hurried back. They both changed into diving gear prepared on site and slipped away with the goods, diving into the sea.