It's called Consuming Capital, also known as stripping the wires for copper, or eating your seed corn. Once the capitalist runs out of "conventional" means to make a profit, they crank up the exploitation dial until they are exploiting themselves. The last two people on earth will be a pair of capitalists trading a lump of coal between themselves.

"Torching the forest to use the ash as currency is a funny thing to base your entire economic system on..."