All living things need to water to survive. This is because all living things are mostly made of water and since they lose water in different ways, they need to get more water to stay the same size. So if a plant does not get enough water, it will shrink. If it goes long enough without water it will die because the plant uses water for a lot of different jobs needed to keep the plant alive.

Water is the single most important thing for living things. Humans, animals and plants are composed mostly out of water and absolutely need it to grow and thrive. Plants need nutrients from the soil, water, and light from the sun to grow and stay alive. If plants did not get water, they would die. How much water each plant needs depends on what plant it is. Something like a cactus or a plant in the dessert does not require as much water as a plant which grows in the rainforest. The two main things plants need water for are turgor, to keep the upright and make sure it doesn't wilt and for photosynthesis.

Plants need water, just like we and other animals do. If we don't have water, we get dried out. If we get too dried out, we die. The same is true for plants, but plants' seeds can live for a long time even if they are quite dry.

I found a scientific paper that says we are just starting to understand what happens to plants when they get dry, before they die.

When plants are making seeds, the last stage is for the seeds to lose lots of water. That's good for the seeds, because they would get moldy if they were too wet. The seeds can stay very dry for a long time without dying.

The plant can no longer get nutrients up from the roots, so the plant dies.

Short answer…it dies. But let's explore that process in a little more detail:
Water is needed for photosynthesis, the process by which a plant uses sunlight to turn water and carbon dioxide into energy! The byproduct of this process, lucky for us, is oxygen. Water also keeps the plant rigid. You may have noticed that when your houseplants are not watered they start to droop and look pretty unhappy. They perk up incredibly quickly when you give them something to drink.