TL;DR Once a ship is successfully boarded and all (and I mean ALL) of its members have been killed, that crew should be considered "wiped out" and they should respawn on an outpost somewhere as they have legitimately lost their ship and any rights to its treasure haul. They shouldn't be able to infinitely spawn on their ship in order to try to eliminate the enemies or regain any captured chests; this makes things too chaotic. Instead, this system woud be in place to emphasize teamwork as shipmates must communicate and organize themselves to have at least one member of their crew stay alive in order for them to be able to spawn on said "alive crewmember". I believe this would put a stop to the greif-ridden situations I experienced today in the following yarn I shall now spin for ye, yarr:
Overall I've had an immensely positive experience playing the game except, really, for one aspect: the respawning system and the chaos it can create. Here's two different situations that happened to me today that illustrate both sides of the coin.
First situation: me and my two-man crew are on an outpost after just having cashed in some treasure and we see that our ship is being attacked and it is eventually sunk. As we didn't have any treasure on the ship to defend or worry about, we just swam to the mermaid to get a new ship, but, we were both killed by a combination of sharks and enemy fire. So we respawn on our mermaid to see that the enemy ship is still there but for some reason nearly sinking as pershaps it was attacked by yet another ship or had the weeping chest. So, we decide to wait around in the water and see what happens. Eventually, their ship is sunk and they need to swim the chests in that have floated up. However, because we were able to spawn on our mermaid and decided to hang around INSTEAD of going immediately to our ship, we were able pick them off underwater with pistols, steal two of their chests and quickly run them ashore to cash them in. Then they killed us. But, seriously, wow. The mermaid spawn-point allowed us to get revenge. Fun? Yes, but maybe not for them.
Second situation: We are heading to an island to find some treasure and we see another two-man ship that is parked in the bay, so, naturally, we decide to sink it. Logical, right? So we thought...We end up sinking their ship, killing one of them in the process and leaving the other crew-member stranded on the island. We find him, we kill him. However, because their mermaid was still in the water, they are able to spawn back in on her and they decide NOT to go to their ship. They decide to stay lurking on the island where we are and where our quest is. Basically, we end up getting killed by them from a clever ambush on their part. We laugh about it and spawn back on our ship which is still sitting outside the same island. We know this time that they are still on the island so we cautiously go about finding them and we und up killing them...again...and this time we are finally thinking that these guys will have taken the option to go back to their own ship and continue playing the game. NOPE. They spawn back on their mermaid, again IGNORING the option to get back to their ship simply to troll us and remain around the island either trying to kill us or steal our ship (which happens a couple times until they realize we spawn back on it and just kill them). So, basically, we can't complete our quest because they would rather troll/grief us. We end up giving up and moving on. I imagine they did the same after realizing we weren't coming back. It started fun, but then got boring pretty quickly.
TL;DR So, seen from two sides, spawning on mermaids after you die and deciding NOT to go back to your ship can be fun for some, but torture for others. Overall, I think it can be taken advantage of for negative purposes and I believe it should be looked at in order to avoid the griefing/loop situations that it can produce. Therefore, I suggest implementing the aforementioned "Crew-Wipe" Mechanic (like that of the Battlefield Saga) that impedes a bit of this craziness.