Let them intervene, it will only internationalize the Baluchistan issue.
And the threat of intervening only helps if the intervening nation has a moral standing among other nations. China intervening in anything these days is not looked at as a favorable thing by anyone in the world. They have 'intervened' in Vietnam, Myanmar, Philippines, Taiwan, K'stan, Laos, Cambodia, and no one is pleased. In fact, Chinese intervention will immediately shift global support in our favor, even by those nations who didn't even know about the Baluchistan issue. China threatening to intervene against us is like a gangster threatening to file a police complaint against a decent man. No one will take the gangster seriously in the police station, so the gangster will only come out looking like a bully and add no moral high ground to their position.
Also, how are they going to intervene? send ships from the SCS > Bay of Bengal > around Sri Lanka > refuel at Djibouti > then to Karachi harbor? It would be ironical if they use the same lengthy route to reach the battlefield which they have been trying to bypass by building CPEC. It's like a vegetarian guy saying "if you don't give me veg food immediately then I will eat non-veg to protest", khao bhai, humara kya jaata hai.
Here's the route China will need to take to reach the Baluchistan battlefield :
There is something in war called freedom of maneuver, China doesn't have it here. India can simply send strike corps from Gujarat and finish the job within 1 week. By the time Chinese ships arrive, the war would be already over. Also note that in addition to the route being long, China will also face resistance form Indian navy. So if a normal cargo ship takes 2 weeks to reach there, a military ship, after all the sea battles, if it survives, will take a month to reach Pakistan from China, with depleted manpower, food, rations, ammunition, demoralized soldiers.
Even the shortest route without any Navy interference takes 24 days.
By that time, our satellites and submarines will have taken care of the Chinese expeditionary force. On top of that, China has announced to send military personnel to help Assad in Syria so USA will want to keep China engaged in another battle to keep them away from Syria. India will not face any resistance form USA if we take on China (even the US wants China to keep away from Gwadar anyway because it is too close to American bases around Africa and Middle East).
If China sends ships to intervene, they will lose their ships, our Unit 22 Tibet strike corps will have landed in Tibet and instead of fighting to help Pakistan, China will be fighting to defend itself in Tibet. Vietnam and Philippines wont be far, and then Japan will reclaim Senkaku islands. China's game will be over. So, China can intervene if it is ready for all that escalation, it is nothing short of a WW3. Is China committed to start WW3 to save Baluchistan?
Lo karlo intervene, we are waiting.