You're referring to something called "demurrage", which is the fair way to disincentivize saving. What the government(s) would do, though, is inflate the currency (print more tokens of it) so that your balance feels to stay "intact" (but the value of it isn't).

By the way, this is what happens today with the USD (or any fiat currency). It doesn't need to be "digital" (it already is).