I think he STARTS Heaps, but if there is any struggle at all, he pulls him for Kaaya. One thing is certain, he has an eye on the future, not just today. It's why he let the D take a beating to implement the D he wants. He believes the D will be better when the guys are older, more experienced, and more talent arrives. Of course, not everyone shares that view, but not everyone is making the decisions. For this reason, I wouldn't be surprised if he starts Kaaya knowing he is the future. He knew Olsen wasn't, but he has to know Kaaya is. He also knows Jake Allison is coming in a couple years, so there's no need in redshirting Kaaya.
One thing to consider is this. How did Heaps actually do when he played in hostile environments? If memory serves me correctly, it wasn't so good. So maybe, just maybe, Heaps is just an insurance policy for Kaaya. Better than an injured Williams who can't play, and better than Olsen who won't work.