You're ideas are good, but the finance is short-sighted.

Saudi Arabia doesn't just short the market, you aren't considering the potential leveraged trades. They would be borrowing cash (they certainly have a lot of collateral) to make big options plays. With the right strategy they wouldn't just make 30% profit. Some far out of the money put options would probably only cost a few bucks per barrel (I'm not looking up the historical volatility data to figure it out), so those could pay off more like 300%.

Of course, there's only so much liquidity in that market, but they can spin this out. Buy put options on other oil and gas companies, and sell the calls to pay for them (synthetic shorts at almost no cost). Find the companies with the most oil price exposure (international shipping? plastics?) and go long on those. Really double and triple down on the oil crash they're going to create.

With that sort of cash injection, and expecting an economic downturn from the oil crash, they would diversify globally as prices crater. Why keep yourself tied to oil, a limited commodity that the international community is actively trying to do away with, and not buy into everything else?