my MacBook pro trackpad and keyboard suddenly stop working, what might be the problem?

I will reverse my advice for a final operation ... one last backup. If they techs want to replace the logicboard and the SSD is soldered to the logicboard you lose your data. Risks all around, but backups are good.

Have tried a force-shutdown (hold the power key)? If so, does it respond after that?

If no response at all, locate a USB keyboard (always handy to have an inexpensive $15 keyboard/mouse around). If that responds, then internal hardware in the issue.

At his point you want to check the bottom of the computer for any bulges. Batteries can bulge and crack logicboard taking out keyboard and trackpad. Check battery condition under "applesymboltopleft > AboutThisMac > SystemReport > Power". If condition is not "Normal" could be the battery.

There is also NVRAM reset if any keyboard will respond: https://support.apple.com/en-us/HT204063 and SMC reset: https://support.apple.com/en-us/HT201295

I am out of ideas now. Report back for others or me to read.

Turn if off now, leave it off. Battery may be swelling anyway. No need to further battery usage. Sometimes it is spilling acid onto the logicboard.

I hope I am wrong in my pessimism. Maybe I am ... I am not a qualified technician looking directly at the device.

Good luck.