Is the power button can be replaced

Here is the volume/power button flex cable: iPad Pro 12.9" (2015) Volume and Power Button Cable

This is a difficult repair though due to the strong adhesive holding the screen assembly in. If you are not confident in your repair skills I would not attempt this repair yourself. It is easy to break the glass trying to remove the screen assembly which is a fairly expensive part. Due to the difficulty of this repair it will likely be expensive at a repair shop.