Note that after the merge any transaction which builds upon one of the newly invalidated double spends will be invalid too. All block rewards are gone too, and any transaction spending them likewise, and any transactions building on them etc.
This is even more serious than you make it sound, and I guess it would kill bitcoin for users of the smaller chain. They might insist on hard forking perpetuating the split with their own custom client or turn away completely. I don't think there is a sane way to reconcile the 2 user bases.
If it did happen, then Chinese users would be strongly recommended to increase their "confirmed" delay for more than 6.
Smuggling the block chain headers would be pretty trivial. Clients should be designed to give a big warning if the block header chain is much longer than the one where they can get actual blocks. The effect would be that all the Chinese clients would show that the chain is unsynced.
Also, on re-merge, the Chinese government might simply define their fork as the official Chinese fork and ban use of the non-Chinese fork. This would be accomplishable by blacklisting the single block on the main chain after the fork happened.
The value of Chinese bitcoins would drop, but Chinese merchants might be more willing to accept them, since they are now officially sanctioned.
