Not sure about the first... second, though, calling back the god is an action specifically performed by critters with priest levels. Takes several turns, usually, but gets done faster the more holy levels you've got directed to it. Doesn't matter if it dies in your domain or not, though (unless the god is specifically immortal, anyway, in which case dying inside their domain just sends them back to the capital.). Just pull up the action menu on one of your priests and set it to call god.
In any case, low HP is one of the tradeoffs for low chassis cost, generally. It's especially bad if you've got low dominion strength (so the pretender isn't getting the much of a HP boost) or it's something that can get diseased without a way to avoid it (really nasty with some of the more human pretenders, when it happens, but rough all around), but, well. That's the trade off. Might not be the best of ideas to take misfortune ranks in that case, heh, or at least keep a good bit of chaff in the same province to soak up event hits. Still not a hundred percent guarantee, but...
Lastly, well, the god dying often isn't that big of a deal, especially later into a game. It doesn't have to be alive for you to win, you just lose out on a pretty powerful tool (usually, anyway.) if it happens.