I assume you're not psychic and can't guarantee that you won't slip on ice and break a bone/ get hit by a car/ suffer complications from swine flu/ etc before the end of March?
I sympathise, it's galling to pay out each month and never get anything back, but that's insurance for you. I keep telling myself it's actually a GOOD thing that I've never claimed on it, because the alternative would be a serious accident or an illness that required hospitalisation (2,500 CHF franchise; gotta be near death before that kicks in). Which it would be silly to wish for, wouldn't it?
I suppose it's actually quite likely that during the two months you could ignore any nagging letters from the commune, especially if you weren't planning to ever come back to Switzerland. If it was me, though, I'd pick the cheapest for basic insurance, get the biggest possible franchise, and sleep better at night!