Yes, it will be a turning point in the war against ISIS because it shows ISIS that they are not safe. An executioner would typically not be the one worried when he performs his job. Now that one has been killed, the thought will be in the back of their minds.
Its like that. ISIS is a virus, and I don't know that we will ever catch up. I'm certainly thinking it will have repercussions through the organization but its not a turning point. There are no turning points in this game. You just keep fighting the good fight and they keep coming out of the woodwork. These people's families friends and values are the only place an outright turning point can be obtained.
If you hit a dog, it learns to fear you. If you earn the dogs trust it will follow you.
ISIS will not run out of fighters if we kill them one at a time. We need to destroy the entire power structure so that they don't have any leadership at all. Soldiers die, then other soldiers get promoted and the military moves on. We've taken out hundreds of "important terrorists" and aren't any closer to actually winning this insane war on terror, almost 15 years later.
No, this will not be a turning point against ISIS. Killing one man will not solve the ISIS issue. The ISIS problem starts with marketing and membership expansion. More young men are joining ISIS because they do not feel that they have any other place to belong. People will keep joining terrorist organizations as long as this is the case. You can't just kill all the terrorists. There will always be more to join.
This will change nothing significantly, at this moment, by itself. One, extremist groups are known for their willingness to die for the cause and have people on hand to fill slots. Second, rarely is anything a turning point with a magnitude on par with the assassination of Archduke Franz Ferdinand and back then they had no idea that his death would start a war that would bring the world to its knees anyway. And, to be honest, this worked in synchronization with other happenings. We're in the "now", so when we look back it's clear that all of that happened, right there, at that time the outcome makes sense. So ,being in the "now" and being in the middle of it I doubt that this is a turning point by itself.