You can think of this a bit like a company that suddenly makes an announcement that they have gone bust. At this moment their shares are worthless - it's the same idea on CelebDAQ.
When we detect that a celeb has passed away their value is set to 0 and trading in them is stopped. They will also eventually be removed from the exchange. If you had any investment in that celeb - you've now lost the lot.
Thats the stock market for you.