I’m not entirely sure why “losing” the original selection is an issue. Your new duplicate is selected, if you need multiple copies, just Shift+D again. The copy of the copy is the same as the original.
If you have some other reason for wanting to quickly and easily select that particular set of vertices, add a Vertex Group in the mesh properties tab, and assign them (in edit mode). This will allow you to go back whenever you want and select these verts, or to deselect them if you need to do that.
Perhaps what you want to do is move a part of your mesh somewhere else? If this is the case, then you would ‘Separate’ that part (it becomes a new object), move the part to where ever you want it, and ‘Join’ the two objects again. If you place it precisely enough (and the mesh has verts in the correct place to receive it) you can reconnect it to the main mesh using ‘Remove Doubles’. Normally, though, you’ll have to connect it up with normal modeling tools.