I would think the legal assets of a non-US citizen inside the US would still be in the name of that person becasue otherwise it would be illegal seizure of ones assets. Assets such as 401(k)'s are not seizable by even the IRS, so I would think that it would still be your assets even if your cease a presence within the US. It might be hard as hell to mange, making it difficult via international phone calls, time differntials due to time zones, ect. But with the proliferation of US companies within China, one might be able to find a US broker that is located within China to "rollover" their 401(k) to, and be able to liquidate without a huge US tax burden.
Due to the US laws concerning property rights, I highly doubt it would be taken away from you.
Legal Seizure of Assets