Mind brain is correct your going to have to reinstall the entire engine itself, it sounds like you deleted some pretty core files, creating a save system is pretty easy so just repeat the process for creation of the save system and or what ever files you had before. Also if you have files you dont want to lose you could always drag the files you need into the new project by putting them in a folder before you delete the old files. Also major thing that a lot of people screw up on is back up your files!! This never happens if you back your data up, go with a git repository, you can go into the git desktop and reset anything you screwed up on and fix any issues such as this one.