Can't vouch for this personally, but the After Effects PM from Adobe posted this yesterday, and several people confirmed that it worked for them:
///
We're getting a couple reports of people unable to launch Premiere, please hold for steps to fix (edited)
This is for Mac:
```- Uninstall any 12.x version (12.0, 12.0.1, 12.1)
- Back up your preferences before the next step (~/Documents/Adobe/Premiere Pro/12.0/Profile-USER)
- Delete the following list of folders:
  ~/Documents/Adobe/Premiere Pro/12.0
  ~/Library/Caches/Adobe/Premiere Pro/12.0
  ~/Library/Preference/com.Adobe.PremierePro.CC12.plist
  ~/Library/Saved Application State/com.Adobe.PremierePro.CC12.savedState
- Empty Trash
- Reboot
- Install the latest 12.1```
(This is not... official guidance but so far it's working?)
Maybe it'll help your coworker. Haven't heard anything majorly bad about the AE update yet.