I don't think this is about the gun at all. At this age, this kid has been exposed to enough reality TV and real life news to know better. His parents should have taught him better and you would think since everyone in the story says "he was such a good and smart kid" he would know better than to threaten law enforcement, or to not comply with their demands. We're not talking terrorists or an angry mob or some strange adults, with whom he may have had doubts whether or not to comply. We're talking about law enforcement. Average law abiding citizens know to comply with the LEO's in a crisis situation-even children. And if not, blame the parents. I am a parent, I have kids from 10 to 22. If my kid pointed anything resembling a weapon at police and refused to comply with their demands of surrender than I would have to accept that he/she brought this end upon themselves. Even if I couldn't understand why they put themselves in that position.
We'll never really know whether this kid's intent was to be shot (thereby committing suicide), whether he was trying to look tough in front of the other kids and not give up to authority or whatever. The bottom line (and answer to the OPs' questions) is; what could have been different is he could have complied. He could have dropped his weapon (real, fake or otherwise) and the situation would have ended without his life being taken. The question is certainly not whether or not the gun looked real or whether or not the police should have been able to tell the difference. It's irrelevant to the situation really. What could, and should have been done is the boy should have surrendered and took his lumps for doing something stupid (bringing something like that to school, assaulting another student with it and refusing to comply with the police demands of 'drop the weapon').
I say all of this as a compassionate parent. We need to teach our children to respect authority. Although I feel for the parents, blaming the police for the way they handled the situation is wrong. If this were an adult at a shopping mall with a pellet gun in the exact same scenario we wouldn't be discussing whether or not toy guns should look real or whether LEOs should be better at identifying threats. We would be talking about what an idiot the guy was and how he did it on purpose and/or should have known better. I feel badly for these parents. I also feel badly for the LEOs who had to make the difficult decision to take this action and who will have to live with what they had to do.
Bottom line is we can't protect our children by removing all the dangerous things in this world. That's like saying the Titanic wouldn't have sunk if there was no ocean. What we can do is learn from this, teach our children to know better and then hope that they put this good knowledge into practice.