I don't believe there are any limits on how long images are retained in your image library. I've got a few that go back years.
Closed listings aren't "Saved". To save them, you'd have to use the Import Listings feature. They do continue to be tracked (appear in Closed Listings) beyond the 90 days eBay can display them. I've assumed for purpose of import, you can't get any older than 90 days from eBay, i.e. no longer than eBay retains them for viewing.
Danno