Minecraft – Will buildings disappear (and chunks change) if I go too far

There are two existing plugins that may do what you need.

• ManualGen allows ops to trigger a structure generation at their location with a command. Strongholds can be place manually this way by your server admin(s). The drawback is that admins who place strongholds will know where they are, which they might not want if they like to explore as a regular player too.

• InfiniteStrongholds generates strongholds across the whole world, in addition to the three vanilla strongholds. This will guarantee that there are strongholds near your spawn, though how many depends on the density value that the admins choose for the plugin. The drawback of this plugin is that Eyes of Ender currently don't detect the new strongholds, only the original three.

The Smooth World option in the Optifine performance settings allows spawn chunks to unload when you are faraway. If you want iron farms to keep working as long as you are in the overworld, turn Smooth World OFF.