As noted, fossil fuels are renewable on a timescale of a hundred million years. We're burning them on a timescale of a hundred years - a million times faster than they are being replaced. Thus, the problem.
A hundred million years is also the timescale for landmasses to move from the equator to the pole or from the ocean to a continental margin. Alaska was not in the arctic a hundred million years ago. It also doesn't have more fossil fuels than a lot of places at lower latitudes. Those are just easier places to get to, so they've already been tapped.
Forests and swamps can become deserts on even shorter timescales - thousands of years. Consider what has happened in the Sahara and in the southwest US since the last ice age.
As others have noted, oil wells are frequently closed and then re-opened when it becomes profitable to do so. Oil wells also can somewhat re-fill themselves: drain the rocks near the well, and it takes time for additional petroleum to migrate in from the rest of the reservoir. But the overall amount of oil present is still going down.
@Rivenburg:
No.
Learn some actual science. You can start with Wikipedia. To summarize with stuff you can trivially learn from it and its sources:
Your most outrageous error here is ignoring what happens when you run objects into each other at ten kilometers per second: they get very very hot. Almost all of the primordial organics in the planetesimals that formed the Earth 4.55 billion years ago were baked into carbon dioxide and water (the planetesimals were not comets, but that's another story). Oil and coal were all formed much later by biology.
Coal is formed by dead vegetable matter - the intermediate form is peat. Most coal deposits currently around date from ~300 million years ago. At that time, the average global climate was warmer and wetter than it is now. Trees evolved to grow into vast swampy forests. Massive peat bogs mineralized into massive coal beds. We know when and how each bed formed because of fossils preserved inside it.
Petroleum comes from a different variety of biological sources, primarily marine plankton, and most current petroleum deposits are much younger than the largest coal beds. Petroleum does not usually occur in the same rocks as coal because of the different source: plankton live in the oceans. Once again, we know the source and age of the oil from fossils in the rocks it forms in (mostly shales). Things do get more complicated since oil is a fluid and can migrate through rock.
Also: Your statement about asteroid impact diamonds in petroleum is nonsensical and irrelevant, as well as entirely wrong.
Diamonds are made in just about any carbon-rich material that reaches the appropriate temperature and pressure. To trace the source of the carbon that went into a diamond requires detailed geochemical analysis, but even that is ambiguous. Shock diamonds are embedded in asteroid impact sites around the world and trace quantities of them can be found just about anywhere. Combine that with the ubiquitous use of many different artificial diamond grits in drilling petroleum wells and any trace diamonds in an petroleum sample tell you exactly nothing about where the oil came from - because the diamonds didn't come from the same place.
Detailed chemical analysis of the petroleum itself, on the other hand, is very revealing of exactly what mixture of dead plankton went into a particular sample and what has happened to it over the intervening tens of millions of years. This is a highly developed area of geochemistry, going back to the 1930s when Treibs showed that chemicals derived from chlorophyll are present in all petroleum samples. Thus, we can say definitively that petroleum is derived in larger part from phytoplankton algae - regardless of how far the liquid may have migrated. Other chemical tracers give a more complete picture.
I suspect that you have confused diamondoids with diamond. Diamondoids are a large class of hydrocarbons, which have one and only one thing in common with diamond: they have three-dimensional cage structures made out of carbon atoms inside of them. A typical structure is iceane, C12H18, named because the cell structure of the single carbon cage is similar to oxygen atoms in one of the phases of water ice. For comparison, even the smallest diamond crystals have thousands or millions of carbon atoms arranged into cage structures following a crystal lattice, with no hydrogen atoms involved at all. The hydrogens and their very small size make the diamondoids soluble in petroleum, while diamond crystals are not.
The carbon-cage molecules have some roles in biochemistry, and detailed analysis of the diamondoids in petroleum shows that they are all made from biological compounds. By comparison, most natural diamonds on the Earth are made from carbon that hasn't been part of any lifeform since the planet formed. Other than shock diamonds, natural diamonds are formed relatively far down in the Earth's mantle (~100 km). That's far enough down that very little biologically-processed carbon gets that far; it's mostly recycled in the upper few kilometers of crust.
