He could be alive, basically because it would make no sense.
He SHOULD have been crushed into oblivion by the pressure when he sank into the ocean. Now, he cant die, but the second Wills blood covered gold piece touched that chest Bill, would have died from pressure (is still in the sea) or from wounds aquired in the sea (such as his lungs and bones shrivelled up into almost nothing)
Now, apparently things that happen in the sea dont count in PotC world, as seen by Jack and Wills lil underwater boat air trick....they wouldnt have been able to keep that boat down there no2
so perhaps hes alive.