Let's say that Brezhnev's health is better and he manages to live to his 90th birthday does the USSR survive longer or does his extended rule cause an even earlier collapse?
some point he would be too frail to fend off the young turks. plus, he did not have the cult of personality like stalin or putin to rule as some figure head
I think he'd have ended up in the same type of role as Deng Xiaoping of China: in power theroectcially, but in relaity little more than a figurehead for the younger officials pulling the strings behind the scenes.
The USSR may fall before OTL. He was on his last legs by the time he died and others were pulling the strings. He was far too senile to be otherwise. The string pullers last a bit longer I guess.