If there is scarcity of a good the supply will be falling and this causes the price to rise. In a free market this rising price acts as a signal and therefore demand for the good falls (movement along demand curve). Also the higher price of the good provides incentives for firms to: Look for alternative sources of the good e.g. new supplies of oil from Antarctic Look for alternatives e.g. solar panel cars. If we were unable to find alternatives to oil, then we would have to respond by using less transport. People would cut back on transatlantic flights and make less trips. Therefore, in a free market there are incentives for the market mechanisms to deal with the issue of scarcity. However, the market can also have market failure. For example, firms may not think about the future until it is too late. Therefore, when the good becomes really scarce there might not be any practical alternative that has been developed. Another problem with the free market is that since goods are rationed by price, there may be a danger that some people cannot afford to buy certain goods; they have limited income. Therefore, economics is also concerned with the redistribution of income to help everyone be able to afford basic necessities.
Without specialization there won't be as vast of types of efficiencies, but I am not sure which type of economy is the most ideal. It could certainly be friendlier without one though. But friendliness can be implemented into other economies as well.
The purpose of the economy is to distribute resources when their supply is scarce, so without scarcity, an economy is clearly not needed. Probably won't happen, though.