As a seller of long-tail, slow-moving items, I have noticed some listings do seem to disappear without notice.
But the timing is erratic.
I have within in the past few months sold items that have been listed for five years , seven years, and in one case since 2013.
I have a note about listing dates on most items.
At one point eBay was adding a Note to items that had been listed for over 16 months. I like that notice. I would take down the listing, check that the value was still correct (stamps have a known catalogue value that rises and falls) and relist as Sell Similar a few days or weeks later, to get a tiny bump in Search.
They haven't been doing that for a while though.
