We don't know, of course, exactly what fate Montresor, the narrator, has planned for Fortunato, but there are several indications that, whatever it is, will be very bad for Fortunato.
From the point at which Montresor tells us that he could take anything from Fortunato except the "insult" that has created such a sense of vengeance in Montresor, we sense that the Fortunato's punishment might be fatal, in part because Montresor appears to be unhinged by his desire for revenge.
When we consider the precautions Montresor has taken to make sure no one sees him and Montresor together--Montresor is wearing a cape and mask, and he has made sure his servants are not at his palazzo--we have to conclude that his revenge will be permanent and fatal. As Montresor and Fortunato descend into the catacombs under Montresor's palazzo, and Montresor makes sure that Fortunato is drunk by the time they get to the deepest part of the catacomb, murder can be the only option--the only question is how.
In a small alcove, Fortunato is tricked into wearing some shackles, which he tries to laugh at, but even he is getting a bit worried. After he's shackled, Montresor uncovers the mason's tools he has stored down in the catacombs and begins to build the wall that will close in Fortunato forever.
Because the catacombs are rarely visited, the likelihood that Montresor's crime will be discovered is nil, so Montresor has lived up to his family's motto--"No one does harm to me with impunity."