Ok, so Google doesn't want us to use the OBI to interface with GV but surely they are still allowing Google Chat to use GV.
If I understand that Google Chat correctly it allows the user to make phone calls from the PC using the PC's speakers and microphone.
Given this, is there a device that I can attach to my PC and turn my home phones into the PC's speaker and microphone. Of course I guess ringing would be a problem. I know this requires leaving a pc on but if that's what it takes to retain my GV home phone setup I might just do it.
If you are willing to leave a PC on, then you can use web callbacks to initiate outgoing calls from GV forwarded to a DID. You don't have to wait for the end of XMPP to do this, it works today.
Sounds like you described the GVmate product. They say their product will continue to work after the XMPP cutoff. The good part about the solution mentioned above by gderf is that incoming calls can be received with the computer off. The web callback solution only needs a computer or tablet/smartphone to do the dialing. GVmate requires the PC on all of the time to work but it allows normal phone use just like what you have now.