In that story, he supposedly needed to be rebonded. Not because one half was "good" (that is, wussy and indecisive) and one was "evil" (that is, impulsive and selfish), and not because these faults seemed to be deepening with time, but because the splitting was having consequences on the physique of both the duplicates, meaning both would die soon.
In "Second Chances", the two Rikers were neither mentally nor physically deteriorating, and if where were any changes in mental or physical capacity originally, those were too slight to be observed.
But there might be legal issues there, or moral ones not yet written into law. Tuvix was an opposite case, a viable and stable merger of two people, and there existed an obligation to restore the two people, as per 24th century morals and perhaps laws as well. Possibly such morals stem from the same thing as the 24th century deep hatred towards cloning or other duplication. Nevertheless, nobody suggests merging the two Rikers... Say, averaging their minds (the necessary transfer technologies are known to exist in other Trek episodes) and killing one of the bodies.