Ultimately, I do not think we have much to fear from China gaining jet engines. If GE will not sell them to them, Russia would eventually anyway. Also, at least by this path we will know what China has in the way of jet propulsion and with their poor standards of quality, I should hope we remain much ahead of whatever they can produce.
This being said, I do not ever really see the US going to war with China. Perhaps we will enter some sort of Cold War type of tension with them, but not complete war. Further more, China's economy, though it appears solid and on the rise, is in reality very feeble and only maintained through manipulation and the suppression of their currency. I look for a Chinese economic collapse in the near future.