This is an interesting question. Since you specify "when Fortunato is silent," your question must relate to a final satisfaction with his deed rather than to a satisfaction with his craftiness in succeeding with his plan to take revenge without risking punishment being brought upon himself:
punish with impunity. A wrong is unredressed when retribution overtakes its redresser. It is equally unredressed when the avenger fails to make himself felt as such to him who has done the wrong.
Poe uses phrasing and vocabulary that creates an image almost as tangible as an actual shiver down the spine--Montresor's and the reader's! The haste with which Montresor suddenly works and the determined silence he now pursues indicate a terror that has stricken to his soul. His ending words, "In pace requiescat!" (i.e., rest in peace) put a final benediction on what he did a "half of a century" ago. It seems from this that Poe is painting an image of constant internal agitation that starts with the jingle of the costume bell and hearing nothing more answering the torch dropped into the cavern.
"Satisfaction" is the (a) gratification of something desired or (b) compensation for an injury or (c) an opportunity to avenge a wrong. We know that (1) Montresor has now succeeded in fulfilling his desire; (2) he has exacted compensation for an injury; (3) he has avenged a wrong. Therefore it must be concluded that while stricken with horror at the culmination of the deed, Montresor does have satisfaction on three counts. What he does not have is "satisfaction" as (d) pleasure or contentment obtained from the fulfillment of a goal!