That is an excellent set of analogies, AWESOME. Only one problem, its lego, both singular and plural. *shivers with outrage*
It's totally probable that there's a way to smoosh the shards together again. and no doubt there's a way to smoosh the bits and pieces of shards back together. It might be the case that we have to wait for all the bits to be brought together before we get any merging, but it might be that, as you said, Harmony may appear, and Sazed may merge and yet break apart into Harmony and Discord... yeah Eric, whachu gonna do? I just said something horrible
It might be that you can Lego them together until you get sufficient legoy potential that the amalgam falls in on itsself and (re)forms an Adonalsium-like lego piece. Maybe Adonalsium was Duplo (kids Lego) and, to grow, it needed to be broken to be reforged... lol