On the Trim Region toolbar, in Boundary edit mode, two commands exist for deleting a boundary. One command deletes the boundary and takes you into boundary creation mode, and the other command just deletes the boundary. These commands do not delete the pcurves. If you delete the boundary using the Home tab > Delete option, then the boundary and its pcurves are deleted.
To delete a boundary:
To delete a boundary and enter boundary creation mode:
The selected boundary is deleted. You can now create a new boundary using the Create Trim Boundary toolbar.
To delete the boundary and its pcurves: