Based on their installation instructions --
LINK -- it shouldn't be difficult to remove and restore to original condition.
Looks like the Voyager rack can be installed directly on the bare roof, or on top of the OEM roof rails. The bare roof has two long black tracks that are flush-mounted to the plane of the roof. The OEM roof rails bolt into holes along these tracks. Or an aftermarket rack can bolt directly into these holes. Or an aftermarket rack can bolt to the OEM rails. Here's a pic of a Voyager rack I grabbed when I was shopping for racks. You can see the spacers used under the mounting points along the black tracks.
Either way, the rack can be removed and you'll be left with either a bare roof or the rails. The rails come in either regular (short) or extended lengths. I have extended rails that I will be removing when (if) my Terrafirma roof rack ever arrives here in the US. The Terrafirma mounts directly to the roof tracks.