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This article will help you tell if it is dead:
https://www.gardeningknowhow.com/plant-problems/environmental/how-to-tell-if-a-plant-is-dead-and-how-to-recover-an-almost-dead-plant.htm

What are the plant's symptoms? This will help with diagnosing the problem.

Generally, yuccas do not require any fertilizer. However, using it sparingly in small amounts certainly won't hurt the plant. I would also suggest using one aimed at cacti or succulent plants. As for cleaning the leaves, they can be kept dust and dirt free by using a damp cloth, but please wear gloves, as their sword-like leaves are extremely sharp.

Yucca do not need to be watered that often--they are drought resistent. Too much water can lead to rotting. Simply give it a good, thorough watering about once a month. If the soil feels rather dry to the touch between waterings, you can go ahead and water.

Yucca, as well as most other plants, require adequate drainage holes when placed in containers. You can either add drainage holes to your decorative pot or put the yucca plant inside a well-draining container and set this inside the decorative pot, placing it on stones (or something similar) to prevent it from sitting in water. Be sure to empty any extra standing water from the decorative pot.

Has it gotten too big for its container? If so, it may need repotting. The following article should be of some help to you: https://www.gardeningknowhow.com/ornamental/foliage/yucca/caring-for-and-landscaping-with-yuccas-outdoors.htm

Water indoor yucca plants only when the top inch of soil is completely dry. Also, do not allow it to stand in water, as this will lead to root rot.