An even bigger loss is just waiting to happen. Despite Trumpās recent acquiescence to a Saudi request for additional U.S. troops, S.A. and her M.E. allies have to be nervous about Trumpās sudden and arbitrary decision to abandon an ally. Even if they trust Trumpāand they shouldnātāthe next administration and Congress almost assuredly wonāt be as pro Saudi as have past policy makers.
So, this may be a situation where supporting/protecting Saudi Arabia is a bad choice for us, but choosing not to protect them could very well be a worse choice. S.A. is not capable of protecting themselves, as shown by the unanswered Iranian attacks on their oil facilities. Without protection the Saudis are practically helpless to counter Iranian aggression and intimidation, as well as being vulnerable to regime-destabilization action from Iranian proxies in Yemen, Syria and Iraq.
Since they need protectionāand if we were not to provide itāS.A. would undoubtedly seek assistance elsewhere. And there is a regime that is able and would be more than willing to assume the role as paid protector: Russia. Currently Russia and Iran are on friendly terms, mostly because Iran is a large purchaser of Russian arms. But if the incentive is great enough, Putin would abandon an ally just as quick as Trump. And the incentive is money. Lots of money.
Saudi Arabia is a huge market for Soviet arms (potentially larger than Iran) and the price for a permanent, protective mercenary force would be high, giving Russia what they desperately need: new revenue sources that are probably beyond the reach of our sanctions. An added incentive, at least from Putinās point of view, would be to humiliate the U.S. on the world stage.
So, what to do? We can continue to protect S.A. until the necessity for oil is nominal (50 more years?), or we can let another power like Russia or China assume the role of protecting the kingdom (assuming they covet such a role), or we can stand down and watch as Iran runs amok in the M.E.