Internal keyboard and trackpad quit working, mac not booting up properly
Firstly, it's definitely worth you taking it in to an Apple Store. I have known Apple to do repairs and/or replacements even when the item is technically outside their warranty period. Of course, each case is different, and it will depend on the What, When, How and Why of your situation. In a nutshell, it doesn't hurt to ask.

Secondly, although it does sound like you know what you're doing, can you confirm you used the correct procedure for resetting the SMC for your particular MacBook? The steps should be:


Shut down your computer.
Keep the MagSafe adapter (power cable) plugged in.
Press at the same time shiftoptioncontrol (on the left side of the keyboard) and the power button.
Let go.
Turn your computer back on with the power button.


Thirdly, since you've now got access to an external keyboard and mouse, have you tried starting in Safe Mode? If so, what happened? If not, can you try it now and report back?

Finally, since you've now got access to an external keyboard, have you tried using Apple Diagnostics? You can do this by:


Ensure your MacBook is plugged in to a power source.
Do a full shutdown of the computer.
Press your power button and immediately press and hold the d key until you see Apple Diagnostics start.
Let the process finish and take note of the results.


Please share your results.