Apparently I didn't need to use an ivr to set up call hunting. It works directly from the call treatment.
The call is handed off completely to CC. I have the hunt timeout at 30 seconds/ext. Callcentric VM grabs the call so gv voice mail is unable to take the call. Even if the timeout is set to 5 seconds each and busy for the last entry, gv still doesn't capture the call because it's already been handed off entirely to CC.
The pc option is only useful if the person is in front of the computer. This isn't the case often.
Missed call notifications are handy, if for no other reason than to know who's calling. Many (self included) these days don't like leaving messages so a missed call alert with a recognizable number (or gv contact name) may prompt a call back. CC does have a phonebook import function but that would be clunky with 100+ entries. That's where gv notifications shine. Alerts generated for a missed call, a vm (+ transcription), texts received, etc.
I don't see this issue resolving as these household members age further, mental function diminishes. I told 'em, either remember to hang up the damn phone or I implement this. Today I get yelled at because no one could get through for ~4 hrs while an extension was off hook. It's unclear if a call was actually placed or the phone was just left offhook. I'm not sure how long a call initiated through gv will remain before reaching some duration timeout. CC allows configuring of this from 30-480 minutes in 30 min increments. Still, even if gv or CC hangs up, the phone is still off hook so we're back to square one.