In the long term, Venezuela has more proven reserves (but much less production capacity). Or nuclear + renewable will overtake fossil fuel. In either scenario, Saudi's share of total global energy production will likely decline by late 21st century.

And in non-oil GDP growth, UAE is currently outpacing Saudi.

As to "everyone there was still as rich as ever due to the oil money", depends on who "everyone" is: 77% of the total workforce in Saudi is migrant workers, many of whom earn < US$5000/yr. They're not citizens.