We did some testing around this with a new character.
Basically, we built a sample base, added a storage container, and did some farming.
We added items into the storage container and left a pick axe on our hotbar.
Results: When leaving the planet the map is not deleted. The items in your hotbar are.
By selecting the same character, clicking on load in the game menu and choosing the map you landed prior to leaving will land once again on teh same map and you should find your base and other stuff on the map.
Myth: So by taking the space ship and leaving the planet the map and your stuff does not get deleted.
The only way to delete a map is if you create a new map and give it the same name.