Will this destroy my current save by replacing everything with lab floors?
No. This mod only makes changes to new areas of the world as you explore them. You'll have no ores or water etc wherever the lab floors are placed.

If I remove this mod will the lab floors disappear?
No. New lab floor will simply not be set as you explore anymore.

If I add this mod, will it replace existing areas with lab floor?
No. This is by design, you are free to have mixed areas as you see fit. Remember that the mod only applies lab floors as you explore.

What's with this "three ways of impossibility"?
Someone getting confused. They thought that applying this mod makes the game unplayable but forget you can always remove the mod or even add it back later as you need to. Just know that if you start a fresh world with this mod enabled then you'll see nothing but lab floors while the mod is enabled - that's the level of impossibility being referred to. Using the map editor you can then add ores as you see fit. You could also use another mod to bring in ores. We've used this mod with worlds using clusterio variations.