We cant sever ties with the prime material plane entirely, that would essentially be suicide. Jochanan isn't the only one whose portfolio relies on them, all of ours do. And even if that isn't enough to kill a god (i think it should be), the lack of activity on the material plane essentially makes the gods dead, in the mortals eyes (a god who does nothing might as well not be there).
I am for the barrier limiting divine meddling. Thus, we can not interfere directly or use any divine abilities on that plane unless it pertains directly to our portfolio (Tocho creates animal, Jemal reincarnates someone, Traume kills someone, Yuneki causes bad luck, etc.). Otherwise, when not pertaining to our portfolio, our power would be limited to that of a titan whilst upon the mortal plane. Of course, we shouldn't USE such power as a titan has if it doesnt pertain to our portfolio, but we will have to employ our own moral restraints with regards to that.
This way, even if a gods war was to ignite, with our power relegated to that of titans whilst visisting the material plane (titans live on that plane anyways) we would not cause any undue damage. Also, this does not interfere with the positive aspects of the game play thus far.