Let's say the internal clamping diodes are perfect and tough as nails, there would be a HIGH all through one alternation and a LOW all through the other alternation.
The point that I was making was that if this scheme was valid, given perfect and tough-as-nails clamping diodes (which is definitely NOT the case), it would still not "zero-detect": Given a 50 Hz cycle, the period of which is 20msec, there'd be a "high" for 10msec and a "low" for another 10msec - it would "positive alternation detect".
In any event, I do not countenance your proposed circuit. Just wait for the components you've ordered.