No, your campaign would not be deleted.

If you wanted to play the original game, or multiplayer, you would have to restore the original files from the 'original data' folder that comes with the mod, or play using the modded values, which isn't allowed in multiplayer. Overwriting the modded files with the originals is as easy as installing the mod itself.

The original campaigns still exist and can be played with the modded values, but I'm not sure that you could continue a campaign. But if you prefer the original, just remove the mod.