Roles and Rates created in the Web TimeSheet is being used for quite some time, probably a few months. That is, these roles/rates is associated with projects and time has been entered against these roles in the timesheet. Now, if the user wants to delete these specific Roles and/or rates, would it be possible?

Roles and rates cannot be deleted when time has been entered against them in Web TimeSheet.

When a role has been created associated with a Project then the user can enter time against the role in the project. Once users start entering time against the Role/Rate in the timesheet, we cannot delete the role/rate.
A security feature of the Web TimeSheet which allows the data protection, stops you from deleting the role/rate associated with timesheets.

If a role/rate needs to be deleted, the time entries that has been made against that role/rate has to be removed. The role/rate has to be removed from the projects as well.