Mormon has left out history that we would love to know. How did we move from the Gadiantons in power to the extinction of the Gadiantons in such a short time? Since Mormon does not tell us, the answer must be speculative, but it can be a speculation based on the known facts of Nephite society at this time period.
We have noted that there had been a shift in the statistical base of the population supporting the new reforms and new ways over a continuation of the old Nephite religion and law. This new reform was the program of the Gadiantons, and it had popular support. The voice of the people apparently removed Nephi from office as the chief judge, and sustained the Gadiantons during the increase in prosperity. As the famine continued, the people returned to their belief in the old religion, and readopted at least the understanding that Nephi was a prophet and he should be a leader of the people. Thus the voice of the people would have turned against the Gadiantons, and toward Nephi and the gospel. Just has the voice of the people had removed Nephi, it appears to have removed the Gadiantons.
We do not know how the total elimination of the Gadiantons was effected. Perhaps they were exiled. Perhaps they were executed for crimes in the civil war. In any case, what we appear to have at this point is a people who have purged the Gadiantons and their program from out of their midst, and have returned to the gospel. It is also important to note that Mormon makes certain that the Gadiantons are not irretrievably gone. They bury the essence of who they are in the ground so that it may be found again.
In the Mesoamerican world there is a long tradition of burying things in the ground that are considered sacred or an offering to the gods. Perhaps something of the Gadiantons was involved with these foreign gods, and therefore they buried something as an offering. Regardless of what it might have actually been, for Mormon the reality of the action is less important that the symbolism of the action. Mormon mentions the burying in the ground not for the burying, but for the finding again. This will become important in the resurrection of the Gadiantons in verse 26 of this chapter.
When we next find the Gadiantons we find them beginning life as a band in the hills. It would appear from this evidence that the true fate of the Gadiantons was exile. Perhaps it was more a flight for their lives. In any case, the explanation of the next arising of the Gadiantons would be that they constituted the remnant of these ruling Gadiantons who were removed from power.