What actually happens to posts when a Lemmy instance shuts down?

When I first new about lemmy, lemm.ee was among the biggest and I created an account on it but didn't use it much and didn't knew that the instance was deleted until recently. So help me understand where content is stored:

• When a post is created, is it only stored on the original instance, or copied to every other one?
• Do all federated servers get a copy, or get posts from other server when user demands them?
• When an instance shuts down, is its content gone forever, or do other instances keep copies?
• If the original server is gone, what happens to edits or deletions?
• Is there any kind of “shared” storage in the Fediverse, or network that store everything?
• Could one still access all lemm.ee content now? Or post in it's communities?