I've thought much the same thing especially around the whole "didn't fight back" point. We do know that the individual shards can empower/invest others at will granting them a portion of their strength either to forward their own agendas, accomplish a specific task, or as an experiment in autonomy. Why then is it not possible that ado simply allowed parts of himself to be invested in others. Just like Tanavast's death wasn't so much a death (at least the first time) and his shattering wasn't so much a shattering. It's entirely possible that Ado is alive and well, waiting and watching what the others do in the background, while nudging his own envoys (wind, rock, night) to his own ends. To some extent the shards control and modify the avatars that hold them, just as they exert some influence on them. All the spren are parts of a greater power, and despite having splintered off, can theoretically (barring the pact) be reclaimed by the shard despite having splintered off. Even if the shattering doesn't include a separate behind the scenes ado, the combined future sight of all 16 pieces (considering the incredible machinations and planning on scadrial that beat ruin - from just a single shard), having the power and foresight of Ado combined should theoretically ramp that up to the 9th degree.
