Person groups can be deleted. Deletion is done in Worktime > Administration > Person groups. Select the person group that is to be deleted, and then select 'Person group information' from the action menu. After that, press 'Delete person group'.
Before the deletion is done, you will be asked to confirm that you want to delete the person group.
If the deleted person group was assigned to persons, will the person group information be deleted from these users. After deletion these users can be found in 'Person non-grouped users' in the person group members list. They can be assigned to a new person group.
The deleted person group can still be found in 'View deleted' view, and it can be restored. If a person group is restored, it will be automatically assigned to the persons it was when deleted, unless they have been assigned to a new person group already.