A good overview of whether the "dissidents" pose a real threat to the peace; with a mass of links within:
In sum, there will be no return to a higher frequency of attacks. Dissident republicans will continue with occasional attacks, such as they do for the past 20 years, with or without a hard border. Hence, all warnings that Brexit "could revive the Troubles" do not reflect existing research.
Link:https://www.rte.ie/eile/brainstorm/2019/0204/1027467-will-brexit-increase-the-threat-from-dissident-republicans/?