The fact that Sokkas sword is lost at the end of the last airbender means it could be found by somone. We still dont know if Sokka had children who could have recovered the sword or if Sokka went back to find it himself at some point. Either way it seems likely the sword will reappear at some point in the possesion of sombody.
I'd like to think Sokka saw a young swordsperson in a village with it training as hard as he did and left it to them without saying a word. Sokka is a class act. That'd be a neat little 8 page story for sure. Comics! Woo!
He already had a boomerang in The Promise. As for a new sword, that'd be really hard to replace, not only because of its distinctive material, but have you seen a Water Tribe soldier/warrior use a sword?