Solution:
Before you update WordPress you should follow the WordPress guideline.
It looks some files are missing related to user_role class. Try updating plugins. If issue not solved try following solutions.
Solution 1: If you have backup then you can restore the website and try update WordPress once again along with all plugins.
Solution 2:
- Create a demo/test location on the server/local computer.
- Take backup of wp_content folder.
- Take backup of Database.
- Install a fresh wordpress on the test location.
- Import the database backup on step 3 to test location wordpress database.
- Replace the content folder on the test location.
- Check, if everything works fine then you can move the code and database to current running server.