@rif3j0qhpi1h This issue has nothing to do with the install; only the save data is affected. If you want to abandon the save, that's easy enough. Start a new save and it should be fine. Just make sure you're loading only that save, that you're not switching between saves at the Main Menu. That should never be done for any reason—it's an excellent way to corrupt the second save you load.
If you'd like to try to rescue some sims from this save, you can save the household to the library and place it in a new save. If you want to keep the house, save it separately. So you'd evict the sims in Edit Town, not with their house, then save them from there, and possibly save the house too if you want.
An imaginary friend that has never animated can be safely object-deleted. One that has animated, as in, you get the "wants to look around" notification, has become an actual sim and can only be deleted with mods, just like other sims.