Deleting a previous saved gameplay

@suecorn13349  Okay, then restoring to a previous save isn't an option.  In the future, it's a good idea to use "save as" to rename the save every so often; that way, the game will create a new save file instead of overwriting the old one, and you'll be able to load the previous one if you run into any trouble.  Additionally, sims you create in CAS will always be in your in-game bin unless you delete them, so you could place them in a different save (including a backup) if you wanted.

Anyway, I'm not sure whether you have two options, or just one.  A sim can ask a vampire to forsake his or her powers, which doesn't always work (it has a better chance if the relationship between the two is high).  But I'm not sure whether this interaction is available with Late Night, or it was introduced with Supernatural.  The other option is to go to the science lab and buy a cure §3000.  To be honest, I've never tried this, but it's supposed to work every time.  Either way, be sure to save immediately before trying, just in case something happens that you don't like.

I asked about mods because one of them allows you to remove an occult state from a sim with a couple of clicks.  But if you're not into using them, then there's no reason to install just to cure your vampire, especially if one of the above approaches works.