If you are still looking for an alternative, https://lemmy.zip/ is a solid choice. Similar moderation policy than lemm.ee.
Monthly reports: https://lemmy.zip/post/39959863
Lots of lemm.ee users moving there: https://lemmy.zip/post/40323214
If you are in the UK (where lemmy.zip is geoblocked due to UK laws), https://feddit.uk/ is a good option.
You can export your subscriptions, blocks and saves from “Settings - Import/Export settings” and then import them on your new account.
As far as I understood, the already posted/federated content is stored by each instance in its database. The pictures/media might be gone but the text should be copied around depends on (de)federation policies
Yes that’s correct, new instances don’t backfill old content. Only the servers online and federated at the time of posting will have the content.
If you migrate to a new instance that wasn’t online or federated earlier it won’t have your old content