Hydroelectricity would be least likely to run out because it is the only renewable source of energy out of the four.
It is generated from the movement of water, whereas coal, natural gas, and oil are gone once you burn it.
Coal, natural gas, and oil were formed thousands of years ago from dead plants buried under the ground so there is a limited source, but the water cycle will still continue for at least hundreds of years.
Hope this answers your question!
-Jabba