1: Is there any flesh on the bones of how he planned on using the tools to do it? Obvioulsy there is more than one way to go about using the Heart as shown during the course of Morrowind's main quest.
2: Several sources claim that other sources claim (already a bit dubious now, eh?) that OTHER Dwemer geniuses thought Kagrenac's plans were too risky, that catastrophic failure could occur. Is there any way of gauging as a certainty whether Kagrenac succeeded or failed? It's almost impossible to tell just by looking, because if Kagrenac succeeded the Dwemer as a mortal race vanish. However, if he failed the result outside-looking-in would be the same.
3: The answer to this may be dependent on the other two. What of the Dwemer who were far away, specifically from Hammerfell? In any event, they vanished as well, but under what circumstances?