How seriously did the Sino-Soviet conflict weaken the Communist bloc?
The Sino-Soviet split weakened the communist bloc in important ways. It made it impossible for the communists to present a completely united front against the West. Perhaps most importantly, it helped lead to detente.
The Sino-Soviet split led to conflicts within the communist bloc. For example, the Soviet Union and China backed opposite sides in conflicts such as the Angolan Civil War. This meant that the US could try to pursue a policy in which it played China and the Soviet Union off against one another. This was in some sense successful in the early 1970s as China sought better relations with the US. This led the Soviets to seek better relations as well and detente was the result.
The Sino-Soviet split did not cause the communist bloc to collapse, but it did weaken that bloc's ability to be strong and united against the West.