You could try cleaning the contacts with a soft cloth like an old cotton Tshirt maybe dampened with isopropyl alcohol (don't use Rum or Tequila, save that for drinking).
It's been said the Keyboard Connector is USB 1.0 but there are 6 pins not 4 like with standard USB. Perhaps there are separate data lines for the track pad, if so that would account for the six pins. This is purely speculation.
I'm not sure what's happened, but it's also affected my laptop. trackpad works, keyboard doesn't. if it weren't for the onscreen keyboard on the surface I wouldn't have a way of inputting text right now.
I have a surface pro 4 i7. The cover (UK English) is driving me crazy!! Every time I start up there are 3 or 4 keys not working - not always the same. Today it is f, I, ) and del.
I try all the usual tricks: power off/on, with/without the cover, clean the connection, try the 30 second press the power switch restart, bang it, kick it.
Eventually I get all the keys working again - until the next time. This is amazingly frustrating for such an expensive machine.