I agree that it's not a good idea to base your entire government on oil revenues, but wouldn't the problem stay very similar if you base the government on the tax revenue of oil production? If then the oil price drops, that will lower tax revenue just as much if not more, because only profits are taxed not revenue
I think diversifying earlier would have been good, using the revenue from oil to boost other areas of the economy maybe even with outside investments, not to immediately give out UBI with the oil revenue, and such