My iphone 6 got got wet and now the on/off button does not work. At the repair shop they said they cannot repair it, its a motherboard issue apparently. Is this possible, is there nothing I can do to fix it?
It's possible. When you say "repair shop", I assume that it was not an Apple Store? If that's correct, I'd suggest you go to an Apple Store. They'll be able to confirm one way or the other.