@rattlyfob you weren't there so let me clarify a few things for ya friend.
Did you think I said to myself: let's get a new bloody boat while my treasure is floating in the water?
My ship was sunk as I was on the Ferry of the Damned, after re-spawning I sailed back to where my ship was previously sunk. So, I didn't have the luxury of collecting my plunder and placing it on solid ground after eating a cannon-ball while on the helm.
My treasure was loaded onto my Sloop in order to sail away and sell it—the chests did sit on the sand for the duration of my voyage in-case my ship sunk while I was away from it.
I've recovered sinking treasure from my crew and other crews in the past, the game has been designed so that as long as we can reach and see the treasure it can be recovered. Once it's been handled again it will be buoyant once more.
So, yes this is a big deal. Players like myself have had numerous instances where the treasure is there, but bugged-out.
Treasure only should be lost when it reaches the flotation timer in deep waters where players can't reach it without drowning due to significant water depth. If it's visible and shallow enough for players to recover the loot, then it ought to persist similar to treasure on land. But at the very least be obtainable when it's within arm's reach before de-spawning.