Getting Vitamin D is essential for your overall health and well being and the lack of Vitamin D can compromise your immune system and eventually kill you.
Usually though you won't die just because of lack of Vitamin D but you usually die because of some other illness and since your immune system is compromised the illness won't be killed off and you'll die instead.
The most common reason people die due to lack of Vitamin D is because they also have Coronary Artery Disease which is aggravated by the lack of Vitamin D.
You should always get out into the sunshine as much as possible to stay healthy and even take Vitamin D supplements if needed.