they are alive!! william helped them to scape!!
Its an expression william uses because they are fishing on a beach. Most people think of the tropics (beaches, etc) as heaven. Sword and Sen are alive though. If you remember one of their conversations, they talked about where they would be and stuff when they got out. For that dream to happen, they needed Williams help.
I still don't understand. There are a lot of contradiction comments. In the end they are alive or dead ? William said that they are fishing in heaven ... Then the last where we see Sen and Sword on the beach is in real life or else ?