Could the Soviet Union and the rest of Warsaw pact undergo Chinese style economic reforms while maintaining authoritarian forms of government and the rule of the Communist parties
In general terms? Yes. Though they needed to reform their system to enact the reforms. (For example, an anti-corruption drive and a purge of the Communist Party.)
In specific terms? No. The Chinese reforms were for a much simpler economy with different foreign pressures and opportunities and a different internal situation.
For example, there's no way the US would let the USSR join the WTO - they didn't even let Russia join. And certainly, the US would be much more leery about allowing technology to spread to the USSR. Further, much of the initial success of the Chinese economic reforms were because of successful agricultural reforms, which meant the largest sector of the economy had a burst of growth. In the USSR, agriculture was no-where near as large a part of the economy.
I could go on. The USSR was not and could never be China. But a well a managed transition to different modes of economic organization is possible.
China in 1978 was a dismally poor nation with a GDP per capita that was 5% of the American level. The Warsaw Pact nations were between 30 and 60 percent, a level China still has not attained. So, reforms would've had a far less dramatic impact.
I love this graph.
fasquardon