The cable just slides out once the latch is raised. You may need to carefully use a nylon stick or a pair of tweezers. Just make sure to disconnect both the charger & power adapter first. Assuming no liquid damage, sometimes keyboards just experience an electronic failure of any number of keys.
Replacing the whole Top Case really isn't much harder since you are removing almost the same parts. When replacing the whole Top Case you will also be removing the Display, Trackpad, speakers & battery. Personally I find this easier & faster to replace the whole Top Case Assembly than replacing the keyboard assembly itself especially since it is nearly impossible not to tear the plastic beneath the keyboard. Of course the Top Case is usually more expensive than just the keyboard itself.
FYI, you do have to be careful with the Top Case Assembly you receive. A client purchased one to fix his laptop, but decided to have me perform the repair. The Top Case Assembly was for the next model year and it was ever so slightly different. The main difference was one of the Logic Board mounting posts was a few millimeters out of place plus I had an issue with another bracket and the right speaker. I was able to cut out the mounting post and use other parts which luckily were still attached to the replacement Top Case Assembly. If you don't notice these small differences, then you could damage or fry the Logic Board.
