As of today. The US military is still allowed to fly assets in and out of Afghanistan via routes crossing SCO member states. They are already moving Al-Qaeda and ISIS terrorists back and forth between Syria and Afghanistan as of now. When the US want to fly In Uighur terrorists from Syria to Afghanistan, its gonna be just business as usual.
It would be nice if the SCO can unite to deny access to US flights in and out of Afghanistan. But I doubt that that could actually materialize. It could create massive tensions with the US and NATO.
I don't think China will have too much difficulty stopping terrorists from entering into the country. What I am really concerned is that terrorist attacks could also happen outside of China.
It has happened before. We must recall the 2015 Bangkok bombing. The attack targeted the Erawan Shrine. A popular tourist spots for ethnic Chinese tourists. Among those killed are Thais, Mainland Chinese, HKgers, Malaysians, a Singaporean, and an Indonesian. All of the non-Thai victims were ethnic Chinese. I was a tourist at Bangkok at that time, but fortunately at another area. I could just as easily have visited that shrine on that day. The bomber was connected to the Grey Wolves Turkish terrorist group who were involved in the trafficking of Uighur terrorists from China to Turkey, and then to Syria. Thailand was just a transit point. The bombing was perpetrated as revenge after Thai authorities caught a few Uighur terrorists and repatriated them back to China.
This is a very real danger if another wave of Islamic terrorism is being launched against China. Chinese citizens and ethnic Chinese could be targeted outside of China. If the Grey Wolves and ETIM could not kill Chinese in China, they can very well switch to target Chinese overseas. Citizens or not.
This is why I feel very angry about what the US and friends are doing with Xinjiang, the Uighurs and ETIM. They are on the path, whether consciously or not, to support and sponsor terrorism that specifically targets Chinese people in China and around the world. And when an attack really does happen, it can be easily blamed on China. The victims be damned. They couldn't care less about Chinese lives. That is pure imperialist evil.
Outside of China. We can only hope and pray that our respective security forces are up for the task to prevent any more terrorism.