The lead-out ribbon from a production quality keypad would not normally come off the keypad on an edge, but rather a 1/2" in from it. The slot is then under the keypad and the keypad is glued over it and so causes no problems.
The prototyping style keypads tend to have the ribbon right off an edge which makes it awkward to mount them in a manner that is asthetic. What I normally do is make a small surround out of thin material, plastic or aluminium, depending on the keypad or project, and glue or screw that on over the top of the keypad. That way the slot is hidden from view and it looks properly finished. It is not always possible to do this though, it really depends on the enclosure or project.
rgds