What was the impact of McCarthyism on the Red Scare?

It's complex. On the one hand, the House Committee report that started McCarthy's downfall made it clear that McCarthy had grossly exaggerated the threat of Communism within the USA and accused many if not most people over the years without any good reason. On the other hand, anti-Communism had been a fixture of US society from 1917 on, even though Communism never had taken root in the US. But it had long been a custom in the US to label many liberal or social projects (such as for instance the law abolishing child labor) 'Communist', and even McCarthy's downfall did little to diminish the general grass-roots feeling against Communism and often any form of 'socialism' or liberalism.

Another factor was that regardless of the end of McCarthy's 'reign of terror' so to speak, the Cold War still was an everyday reality with its ever-accelerating nuclear arms race.

So although many Americans felt a little ashamed to have seen Communists under each and every of their beds, the Red Scrare remained until after the fall of the Soviet Union around 1990. The funny thing in hindsight was that the Russians - who had lost several times more lives than all the other Allies taken together in WW 2 and who had seen direct American involvement with the forces fighting the Russian government it its civil war - were as scared if not even more scared of American agression and domination as the Americans were of theirs.