Should Tree Lilies be cut down before winter or left as is?

Answer 1

They will be left until they are completely dead. Cutting them while they are taking those nutrients back into the roots will be detrimental to the plant's health.

This article will give you more information on the care of these plants: https://www.gardeningknowhow.com/ornamental/bulbs/lily/growing-tree-lily-bulbs.htm