I think about this because there are a couple of ultimates that can be suddenly stop and do nothing, and that can be really painfull.
The first is Violet, the one who is able to shield your whole team with her ultimate, but if the ultimate is activated right before you are going to get hit by an basic attack or an enemy skill, she suddenly stops and do nothing. and you end up wasting your whole energy bar just to do a little jump back.
Another one is Mike, who can also get stop and deals no damage if he gets hit right after he use his ultimate, again losing all the energy and doing nothing.
I think there should be some way to fix this, for example, if zurg uses his ultimate and get stop (by a hit or a cc) he still had his energy bar almost full.
So. there should be some way to improve this. for example, making the hero unstopable at the time it cast the ultimate (Unstopable against damage, still stops if the hero get cc or dead). or maybe refill some of the energy if the ultimate got canceled for any motive.