The mask is removed but the clips on the image(s) are preserved. After you convert a mask to image clips, you may need to manually show or reload any images that were hidden or unloaded by the mask. To show images that are hidden, you can select the image frame, then right-click and click Show Image on the shortcut menu.
You can then use the AutoCAD IMAGECLIP command to turn off the clips and change the clip boundary if desired. Any image that you insert into the drawing after converting a mask is visible.