Well, based on Indian and supposed Russian sources, Russia suspended S-400 mainly due to Chinese espionage and Sino-Indian conflict. However, since China already possesses the S-400 systems, reverse engineering and adding more Chinese elements in them (like chips, AESA radars, etc.) to crease a "HQ-400" is not longer an issue for China. China could also dissect and reverse engineer the powerful solid fuel rocket engines of the 40N6 missiles (if China already possess it) for other uses (say a new terminal-phase ABM). Thus, the Russian espionage charge is useless in preventing the Chinese from getting their hands on the S-400. Nevertheless, should Moscow officially side with India, the U.S., and Japan in the upcoming geopolitical great game, it would be a tragedy for Beijing. Given its long border with China and its lack of rule of law domestically (say police and skinheads killing Chinese students and business owners), Moscow could cause some serious damage to Beijing on a daily basis, and Beijing would have to play a three-front great game. You would probably expect the EU to come to China's aid under such scenario. Yet, European countries are too ideologically proud (similar to Washington) to deal with the Chinese on an equal basis.
