I doubt he cares about that tbh. Plus he was the one who won the Brexit referendum, those who wanted that to happen will welcome Cummings with open arms.
Well if you wanted to destroy the UK, first you'd sever it's ties to the EU. Expose the gripes between all 4 nations with a culture war, then you'd attack the UK Government with leaked messages and other data. Then you'd move onto breaking the Union. Thus taking the UK out as being a major player without having to fire a single shot. And whatever's left of the City of London can then be used to launder money with impunity.
Cummings might be a double agent for Russia or he might just be as somebody said on twitter a chaos goblin. In any case, the Tory Party has compromised itself by accepting donations from Russian Oligarchs, who have to keep Putin happy in order to stay alive. I expect Boris Johnson's jaunt to Italy to party with his Russian Oligarch friend without any security with him, likely means the Kremlin has kompromat on Johnson.
Someone else was working with Boris before Boris became our Leader - Cummings didn't join Boris until later.
Far-right activist claimed he helped with Boris Johnson’s resignation speech as foreign secretary
But Cummings did lead us toward the herds of unicorns running free on the sunlit uplands.