Now that is a question that i hard to answer. It would take a very serious minded government to make the changes. It is not just a matter of passing laws and enforcing them. It requires educating the masses and changing the culture and traditions of the society. I am old enough to remember the educational program the US government did in the 1970's. Remember the crying Indian commercial. And, we were reprogrammed in school about litter and pollution. "Give a Hoot. Don't Pollute" from Woodsy the Owl commercials were very effective too. China would have to do what the USA did and multiply that to make an impact.

No need to panic.  Mother nature is good at recovering.

I grew up in industrial Scotland in the 70's. Just as industry was coming to an end. The local river was a different colour every day.  The ponds were covered in oil. There was not a lot of wildlife in the water at all.

The factories shut down, and within 10 years salmon were running the once dead rivers.

If you are a young westerner you probably have not seen pollution in your home country.  At least, not in the scale you see here.  But believe me, western countries were just as bad in the past.  The London smog of the late 50's resulted in an estimated 14k deaths.

And lets not forget that China is not the only polluter in the world.  It has only recently become number one.  That means that number 2 and number 3 are not far behind.

Yes, nature will always cure its scars, no matter how badly damaged it is, but if you let it do this might take thousands of years.

Now if we are talking about man made cleaning it can be done, the technology exists and China has the means to do so, but it will cost hundred of billions if not trillions or RMB and the real question is who is going to pay for this?

There is no solid "no return point". Environment keeps changing, with or without human activity. Species appear and disappear, climate evolves, etc...

Air quality is the "easiest" one to fix : quit burning so much coal in so little time. It means switching to other power sources (takes lots of time and money), and using less energy more efficiently. We talk about major infrastructure change, in time of fast declining growth. So the change will be slow, and even slower than that, due to problematic rule of law. So it can be fixed within a decade, at an enormous cost, or a few decades if we are more realistic. Soil and water pollution can be really tough one... Desertification, the only fixes takes 50 to 100 years to show some effect, when it works. Often, it won't be back to the original state, it will just a more live able state.

It's doable, but with an extraordinary collective will to do so. So far, collective will, public conscience, civil society are ideas that are actively fought in China. "It's foreign, it's an attempt to destabilize and control a China", this kind of paranoid delusions. Short of this, there will very belated half-hearted attempt to curb the appearances of pollution... With people not even able to police themselves to use a garbage can.

Let them run themselves into the ground for all I care. Then, and only then, will the ccp even consider improving the environment, because "make fast big economy for harmonious society"

They have the possibilities and money to protect the environment for really long time. they do not want to go this way because it will shrink the numbers on paper and income in high positions.

 Industrial chimney filters are widely available, but no one buys them here. In EU are forced to each industrial chimney under high penalties. guess what happen. blue sky with sun...

Industrial cleaning of waste water BEFORE releasing into rivers, and significant part of the water is recycled and used in central heating for towns, for example.

Insulation and all other things are going more strict, as for example hover machine now is forced to use with maximum power of 800Watts, so it save energy and producers are forced to develop better ways to suck dust with using less energy. lot of improvement was already done.

 Whats going on here ? international companies with solutions to degraded water sources for improving quality of water are forced away from china with their technologies. roads are cruised by diesel trucks 30 years old, with none filters and low efficiency engines, just for the sake let the economy is running in nice numbers. Buses waiting in end stations for their next run for 20 minutes with running engines, because " it cost less then broken engine, if you often start and stop engine" .