Anyone who has done a rootfs+eMMC reflash and their device still doesn't vibrate definitely has a dead vibration motor. Replacing it is a pretty serious bit of hardware work, your best bet would be to remove the motor then go to a cell phone shop to find a suitable replacement and solder it back in.

Some people have gotten more life out of failing vibration motors by using a script to run them for long periods while shaking the phone to shake debris out of the motor.