I'm guessing immortal in this case just means the snail and I would never die if something doesn't kill us, but that external forces can still cause death. If that's not the case, I have no reason to worry since the snail technically wouldn't be able to kill me. If that is the case, I'd just build a house on top of salt deposits. Good luck, snail! Or I could just play it cautiously and regularly check for the snail and if I find it, just up and move somewhere else. It'll take some time to catch up and there are plenty of predators between me and the snail in the meantime.
He took the lethal snail poison in your place? Surely he shall be missed. At least now we don't have to worry about how many bananas to eat.
I'd just live life and put cups over every single snail I ever see from this point on in case one of them is the deadly one. They're probably decoys, but never hurts to be sure. It should be easy to live life carefree without encountering this snail? Just keep moving around the world and it should never find you!
One thing that really confuses - and concerns - me is that why does this snail have to be so vengeful? It doesn't profit by your death as it already has all it wants. So is it advancing towards you for a separate reason, or is it merely some snail automaton that is controlled to move towards a stimulus? I'm confused why the snail has to try and move towards one person instead of just doing snail things.