Some nonzero percentage of all businesses ever started have not failed yet.
Although if I guess what the parent comment is thinking of correctly, there was a piece on HN fairly recently about how businesses that were doing well but closed were counted as 'failures'. E.g. the owner retired and closed, the owner got ill and closed, the owner sold up and the business was merged into another before it was running for 5 years, etc.
That being said, it's nothing like 20% so clearly there is an implicit time frame.