It can be the final push because we are already on the edge. It does not mean Brexit alone sends the economy into recession. There are typically multiple reasons for recessions, not just one.
If we are "on edge", that means there is bubble. If there is bubble, then anything can push it "over the edge" and not necessarily this Brexit although it would be scapegoated to be the cause. Like I said before, with any changes, there is always something good, something bad and Brexit is no different. The important thing here is to try to adjust for the bad and work with the good and then everything and everybody would be better off unless you are like Soros who just wants to profit over the "bad" then yeah you would have every incentive to paint the doomsday scenario.