There's never going to be a moment when we squeeze the last drop of oil out of the Earth's crust. It's just going to keep getting more expensive as we drain the easier sources and have to look harder and drill deeper in more and more remote areas.
As for water, there's plenty of it in the ocean. All you need is some cheap energy to desalinate it. Californians need not worry. One of the richest and high tech economies in the world sitting right next to the largest reservoir of water on the planet. They'll figure it out eventually.
I'm not saying it will be easy. But the combination of large scale investments in making renewable energy generation dirt cheap and increasingly more energy efficient ways to desalinate water inevitably means that people will have access to as much water that they need when this gets pushed far enough. Just a matter of time. Lots of places manage to get by with desalinated water already. Large parts of the middle east for example. It's just about making the process cheaper and more efficient.
Also this seems like it would be more of an issue in shallow waters than it would be in open ocean. A simple pipe to deeper waters probably goes a long way to fixing things. The Pacific is pretty deep near the Californian coast and has strong currents too. The volume of water moving through that is probably many orders of magnitude larger than any brine you can dump there. So, unless I'm very wrong about this, I'd expect things to dilute pretty quickly.
Let's say that you have an oil field that contains a quantity of oil that, when burned, would release X megajoules of energy.
The oil company consumes Y amount of energy extracting, refining, and transporting that oil.
At the moment, Y is less than X, but Y is getting larger relative to X. Once Y and X are sufficiently close, it's no longer energetically worthwhile to pull oil out of the ground.
However, try to design an aircraft using natural gas, batteries, coal, hydrogen, etc and you run into huge issues.
In this scenario, oil power plants can't operate anymore anyway, so demand for oil probably gets relegated to stuff like classic cars.
Edit: why Germany is now so troubled about Russian gas? Not because they'll freeze, but because the choice is to either freeze or shut down most of the industry. Which you can't just spin up in a couple of weeks.