Think of the Sun as a giant battery which gives power to the plant, and the cow eat the plant so the energy get transfer to the cow, human eats the cow, the energy get transfer to us. In other word we would all die.
When or IF the sun dies, all the plants on earth will die and no plants will grow to replace them. The earth will be uninhabitable, we will all freeze to death, and the earth as we know it will cease to exist.
The sun isn't large enough to produce a supernova. When the Sun begins to die, it will first turn into a red giant, swelling to the point where
it is as large as the Earth's orbit. Then it will collapse on itself, forming a white dwarf.
If it goes nova, the planets will be destroyed in a huge, fiery blast. If it goes cold, then we will eventually freeze to death. Even if we find a way to stay warm, the plants and animals will die, which means that our oxygen will be lost.
The sun will form a red giant, either engulfing us or burning our civilization to death. After this, it will die out completely, voiding us of heat and ensuring our planet becomes uninhabitable by organisms as we know them.
Although the Sun is a star, it is not large enough to go nova. It is more likely to expand and get hotter as it gets older, eventually swallowing the Earth after baking it.
I think that we will find a sensible solution and we will find a way to keep the human race going. Hopefully, the only thing that we can do is wish for the best and try our hardest in life.
