If it looks like its dead, its probably dead. Cedar retains its needles all year long. Larch is the only pine that looses needles in the fall.
If the wood is still "sappy", it will be OK for lumber. I have sawn yellow cedar that has been cut for over a year, and the lumber was OK.
What type of cedar is it, and why did it die? Eastern red cedar will be good for many years after being cut. The white sap wood will rot, but the red heart is worth much more. Sapwood is considered a defect.