Keyboard and Mouse randomly cut out and stop working.

Because of the way the trackpad handles the signals (it takes the keyboard signals and daisy chains through itself to the mobo) you most likely need to replace the trackpad itself and you should restore functionality. Does your power button still work?

I’ve the same problem (many years later). The keyboard ánd trackpad stopped working at the same time. Nothing seems to work (like PRAM and SMC reset). External mouse and keyboard works fine though.

I’ll try to replace the trackpad flex cable. And I hope it will do the trick. Apple says I should replace the top case. But I’m not sure why that would solve the problem.

Edit: I replaced the trackpad (with the original cable), that worked! Both keyboard and trackpad work fine now!