Rohm was never the leader of the Nazi Party, only the SA. And TBH he was probably more of a nutter than Hitler was.
If he somehow managed to catch wind of the Knight of the Long Knives and launch a counter coup, killing Hitler and replacing him as head of the Nazi Party (but not the Chancellor which would devolve down to Von Papen as Vice-Chancellor), it would probably end the entire existence of the party. There would be a major schism, the SA would follow Rohm, Himmler, Goring and the SS would split off, and in the ensuing chaos President Hindenburg would have no choice but to dissolve the Reichstag and call new elections due to the assassination of his Chancellor (the office of Fuhrer did not exist yet). The implosion of the party would mean a respite for the Weimar Republic, the Far Right being discredited, and with the Far Left in disarray since the forced liquidation of the KPD a year earlier, it would be left to what could be gathered from the SPD and others to form a new government.