More on Reinstalling the macOS:
Nothing would be deleted. It's just that items that have become corrupted or deleted, would be replaced or reinstalled back to where they should be. Go Here: How to Reinstall macOS from macOS Recovery - Apple Support
Important:
Create a Time Machine Backup First:
Prior to the reinstallation of your macOS, be certain to backup your Mac using a Time Machine Backup. That way, you can have something to restore your Mac from, should anything go wrong with the reinstall. Use an external hard drive that is at least 1.5 the total storage capacity.