When a runner is properly installed, and ultimately removed – the stairs will likely need some attention. However, hardwood can very often be restored to a nearly like-new appearance. Depending in part on how long the runner was in place, that work may be very little or may need refinishing. Keep in mind that a staircase which had no carpet over that same period would have suffered wear or damage to the finish from foot traffic, and would require work or refinishing.
It is important to understand that runner installation on a staircase must first of all be done with safety in mind – a runner installed using some sore of half-measure will likely result in a runner that is not safe. Installed carpet should always be tight once installed. It should have virtually no movement once installed.