Minecraft data is stored in a mix of JSON and a well documented/understood custom format. It's even documented in the same wiki that players use to learn how to play: https://minecraft.fandom.com/wiki/Anvil_file_format
The world files are saved unencrypted on disk and can be backed up, edited outside the game, and even converted easily to another format if another game somehow dethrones Minecraft in this niche.
There are also a variety of viewers that render Minecraft worlds to map images or interactive maps a-la Google Maps.
Finally the official Minecraft launcher allows players to choose any archived version of the game instead of forcing the latest and greatest. The only missing versions are very early development builds from 2009/2010. This ensures that even if a newer Minecraft version is released that is incompatible with this effort, the last compatible version will always be available. (Players can and do archive these versions themselves as well, this is not reliant on the official servers)
