I think a mix of anticipation, disgust, and disbelief. I really haven't had any reaction to Aaron dying yet. I usually have to read books five times before I'm like wait they DIED!
Mostly I think I'm apprehensive for what's to come next because I love Call but I really don't think he's smart enough to realize that things will only get worse for him if he escapes. I mean if he stays in jail it'll probably take a while but he can probably convince everyone that while he is Constantine Madden he doesn't remember being him. Also he can get Tamara to vouch for him that he didn't kill Aaron. If the Masters hunt down Alex it will probably become immediately obvious that he now has chaos powers, but it would take Call staying in jail for that to happen.
It will also be interesting to see if now that Call and Alex are obviously enemies if they end up in a battle to the Death like Constantine and Verity Tores.
I don't think Call will try to bring Aaron back both because he would be to afraid to try and despite gaining a better understanding of him he still does not wish to be like the Enemy of Death. I could imagine something happening that would change his mind about one of those things. I do think that Aaron will come back some other way though maybe if Call has some internal changes that give him more grit to do that.