I can't imagine it. In 2018 the CPC is nowhere close to collapsing. China is going to become the world's #1 superpower before 2040. Living standards across China will continue to rise. The CPC is going to be riding this wave for a long time. Possibly for over a hundred years. Even when living standards one day stagnate, and China's global influence starts to wane, the government won't collapse over night. It takes time for dissatisfaction to build up enough for there to be a revolution. I don't see any realistic scenario where China is a multi-party democracy in 2040.
Who said anything about collapse or revolution?
Someone I know who is a Chinese citizen studying here thinks the PRC will transition to multi-party elections within 20 years.
Assuming they suddenly decided to be more democratic, I don't see why they they would go straight to multiple parties. Instead they could try to play it safe and allow the already existing multiple factions inside the Communist party to formally organize themselves.