Dan's Answer to a similar problem in 2014: Give him credit if it works.
The keyboard/track pad ribbon cable from the top case is not seated correctly into the logic board connector (or damaged).
Something was spilled into the keyboard and it took a bit of time to damage the connections.
The last possibility is the battery has swelled pressing from under the keyboard causing it to fail.
To test for the battery problem, put your laptop into a plastic bag making sure to pull out as much air out as you can. Place the laptop into your refrigerator for about an 2 hours to drop its temp. Take it out and quickly turn it on, see if the keyboard and track pad are working. If they are the issue is the battery pressing on the top case from below.
If your upto it pop off the bottom cover to inspect the ribbon cable to see if its correctly seated. Otherwise you'll likely need a new top case as the keyboard is part of it.