After destroying the Trident of Poseidon, Salazar and his crew are
returned to their mortal forms with their curse finally broken.
However, without the power of the trident the walls of the ocean
slowly started to fill in the area threatening to drown everyone.
Fortunately Jack, Henry, and Carina grab onto the anchor line from the
Black Pearl, with Barbossa attempting to lend a hand. As they run,
Salazar still bent on revenge pursues them while his crew run to the
anchor to save themselves. http://pirates.wikia.com/wiki/Pirates_of_the_Caribbean:_Dead_Men_Tell_No_Tales
At some point after Jack freed the merpeople, the Trident was hidden
in Poseidon's tomb, an underwater grave off the coast of an uncharted
island. By this time, those who knew of the Trident believed it could
no longer be found. However, it was also revealed that the Trident
also possessed the power to break any curse at sea. Because of this,
the Trident was sought by several parties: Armando Salazar to have his
revenge on Jack Sparrow, Henry Turner to free his father from the
curse of the Flying Dutchman, Jack Sparrow to save himself from
Salazar, and Hector Barbossa to reclaim control of the seas. With the
aid of Carina Smyth and a journal given to her by her father, the
island is located and the Trident revealed itself by parting the
The theory is that Tridant didn't just undo the immediate curse of the story---but several---so it serves as a kind of "reset" within the ongoing story. -- Which means, if Will is no longer the Captain of the Flying Dutchman, then the ships' predecessor Davy Jones again is, because "The Dutchman must always have a Captain" and so far it appears there is no way to destroy the ship and/or to know if there is another way to ferry the souls.
Yes, one of the Trailers states, "The Final Adventure Begins" implying that Dead Man Tell No Tales is the first in a series of final films for Pirates of the Caribbean franchise and implying that they are not perfectly stand-alone, but interrelated.
EDIT: I found the trailer with "The Final Adventure Begins" is stated between shots @ 1:51 + 1:57 minutes marks.