Greenpeace on the roof

Are we really hoping that by the time oil reserves are depleted, some new energy source will be found?

hoping is what the entire oil industry does. it hopes to find more reserves like Saudi (unlikely) and hopes that a new equivalent to oil as an enegy source will be found (unlikely).
Frankly i don't think they even care, especially the highly paid company controllers, as long as the money keeps rolling in and their pensions are up to date.
The future as i see it involves very expensive (very rare) oil vs very expensive alternative energy sources battling it out head to head, which is interesting since it will force all to use less and become more economical in almost every way.

Eventually oil will become much more expensive than the alternative energy sources and oil will be relegated to the history books.
But still, the alternatives will still be very much more expensive than oil and laughably, at the moment,most of the alternatives at some level or other depend on oil or gas for it's current production cost. Without oil it's likely to be even higher.

Energy is important now, and we all know it, of course, but it's a given commodity we all take for granted.
The future will have much more focus on energy in everyday life, because it will be a lot more difficult to get.

As always the poor will suffer greatly whilst the rich will plod on as normal. That at least will stay the same.
I myself don't want to be around when much of the western world start bullying the other countries for oil in desperate need for oil that our economies and social structures rely on so heavily. I have a feeling it ain't going to be nice for anybody.