This is a great question, but a complicated one. If there are no plants because the Sun exploded and is no longer providing light and warmth on Earth we would definitely all die. The amount of energy the Sun provides the Earth is indescribable; it is the driving and sustaining force of this planet and, pretty much, the whole solar system. The Sun may explode in millions of years when it starts running out of helium and hydrogen to burn, but humans may not even by around to really witness it. Also, there are small chances that humans will even be able to survive the explosion.

Now, if you're thinking that just the plants die and the Sun is there, it's tough because can't the Sun help to grow more plants after the existing ones have died? If there are no plants on Earth then we don't have enough oxygen to live, animals and humans don't have the necessary food to eat, and certain microorganisms which are the basis of our planet do not have a habitat - just to name a few things. If you say, what if humans only ate meat, well think about it. Most of the animals we eat are herbivores, and if they don't get their necessary nutrition to live then we can't get ours either; the whole food web will be messed up. You could bring aquatic life into this too because there are plants in bottom of the ocean.