They remain indefinitely. Sometimes the asker will get tired of the notifications and simply remove the question so it disappears.

Hi Randy, You can find them in Catalog Home>Community>Questions if you want to review them. Also they're at the bottom of each product a question was asked for in the reviews.

If the original poster doesn’t select a best answer I think buds will give credit to those with correct answers. As far as zero answers I think all questions have some attempt at being answered whether the answer is correct or not.