By disabling the Vanilla datapack, and closing the world, players will find themselves unable to re-join the world without the game either automatically re-enabling it, or giving players a message demanding to enter the world in "safe mode". Also the datapack i had enabled in the world was said to be broken afterwards, even though cutting/pasting it in and out results in it working again perfectly fine. Renaming datapack also claims to fix it, but error comes up again upon re-loading.

Edit: It's worth mentioning that the error box still shows up when I remove my custom data pack from the world file.

First image shows me disabling datapack. Second shows it reenabling itself after rejoining.