1) China would be much better off initially, and the GLF and CR are both Mao's pet projects, so if he had died somewhere in the early 50s China wouldn't have had them and probably have looked more like post-Stalinist USSR. The economy would have being ran by Liu Shaoqi and Deng Xiaoping. On the other hand, without the trauma of the CR/GLF, there might be less impetuous to reform agriculture after 1979 and therefore kicking off reform and opening.
2) The idea that Lin Biao was trying to launch a coup has being thrown into serious doubt, most likely he was never attempting to actually implement plan 571.
3) Depends on when