... In the long term.
In the short term, it's going to be very, very bad for them indeed, as the sole source of foreign exchange goes away and the ordinary folks find themselves abandoned in a climate-change-drought-crippled land that has become populated well above its agricultural carrying capacity, and the elite jets off to enjoy their stolen wealth in Switzerland.
There was a recent HN article about Israel's progress with desalination[1]. Obvious funding issues aside, I wonder if that approach could ease some of the water issues?
Perhaps that kind of investment would be a good use for the oil income, whilst they've still got it.
It's not like they would not see it coming. Petrol is eventually going to become too expensive at some point, and they should invest accordingly. But numerous past examples of countries relying on raw resources have shown they usually don't adapt and plan, so I don't have too much hope in their case either.
The rulers are doing fine -- they've got armies and secret police and offshore investments so that when things turn to shit they can just jet off into exile like the Shah of Iran.
The ordinary folks don't have the money and they don't have the oil, they stay quiet for now because they don't want to be imprisoned or executed and because the rulers spend a small chunk of their surplus on social security.
In other words, the people with money to invest don't care, and the folks who might care are in no position to take action.
https://en.wikipedia.org/wiki/Resource_curse
We'll stop meddling and making things worse. The leaders of those countries won't be able to substitute oil wealth for popular support or funnel money into pushing Wahhabism.
It's the best thing that could happen to them.