Sorry if I sound blunt, but absolute "zero power" is not a realistic requirement, especially when the circuit is up and running. The rest of the circuit will draw significant current anyway, so it makes no difference if the reset circuit contributes a fraction of a percentage point.
Even when the circuit is in reset, it will still consume a certain amount of power, most likely far more than a good reset circuit. Do not forget that when in reset, the oscillators of the micros do not stop, and since it is the switching action that leads to power consumption, the rest of the circuit will draw significant power, even though it is in "reset".
Second, you say you do not want to use a comparator, but on the other hand you need brownout protection.
These are conflicting requirements. So you will have to compromise somewhere.
VVV