The home button is not going anywhere anytime soon. I think they would rather change the size, have a smaller home button or have hardware that wont wear as much. So they might have a touch panel on the front that accepts your finger input like the clickable trackpad on MacBooks. The gesture is nice on the iPad, I haven't touched my home button in over 5 months. However on the iPhone screen it's just so small especially if you consider people with huge hands and the fact that it requires all your fingers not just one or two.
The volume buttons will also always be there because not everyone uses they phone with headphones. Even people who use headphones use the phone without them at some point. If you are thinking using software then you are requiring two or three taps when a simple hardware button only takes one. Just look at your TV, how long have TVs been around and they still have volume buttons.