Only in economic terms. Sure, China would face a massive shortfall and would have huge unemployment if it suddenly stopped exporting to the USA. But that's not the same world of trouble as suddenly being unable to get important technology and parts, which is what the US would face. And China is really not reliant on imports from the USA - especially not in time of war (that is, they might have a problem selling things legally without paying various royalties to US companies - but that doesn't matter anymore in a world War).