A billion barrels of oil is a drop in the bucket. The appraisal of Unocal's reserves has been dwindling quickly in recent years. They sold off the best ones, and are left with the most expensive ones. That's why the company is valued so low.
If we go to war with China, Unocal's reserves will be worthless, because as you say, they are in Southeast Asia, for the most part. They will be knocked out on the first day of the war.
We'd be much better off letting the stockholders sell these reserves to China when the price is high. If they want to, they can invest their money in other reserves, or you can invest your money in other reserves if you think it's such a scarce commodity, and they don't.
The notion that we should tell stockholders who they can and who they can't sell their stock to does not appeal to me when all we are talking about is a oil reserves. Many Freepers are always talking about how the world is awash in oil. I don't really agree with that, but it's not so rare that we should tell China that we aren't going to sell oil to them when they are willing to pay us a premium over the market price. To do so would accomplish nothing.