Schrödinger stated that if you place a cat and something that could kill the cat (a radioactive atom) in a box and sealed it, you would not know if the cat was dead or alive until you opened the box, so that until the box was opened, the cat was (in a sense) both "dead and alive". This is used to represent how scientific theory works. No one knows if any scientific theory is right or wrong until said theory can be tested and proved.
In one of the previous episodes, Monroe talked about Schrödinger's Cat and what the theory meant. If you look at the moment that Nick starts back through the mirror: The portal is the top of the box. If it isn't opened, two realities can exist. Actually, and infinite number of realities can exist (who lived, who died and combinations thereof). So, Nick jumped into a reality in which everyone dies. Once the Zorester is dead, there is a path to the other reality where everyone is alive before the events happened. Zorester took Nick to one reality but the stick dragged him to another, better reality. It isn't a timeline like Star Trek. It is like only one reality can exist at a time, but until it happens, an infinite number of realities are possible. Zorester made it possible for Nick to experience the reality most likely to make him give up the stick. That is incredible power to make that happen. With Zorester gone, the other reality asserted itself.
Now the whole "Blood of a Grimm" thing is more problematic for me as it wasn't earned in that no hint of the spell being about more than the poison. If the room had flashed or changed color, it could have signified that something more than poison was in play. But, we are left scratching our heads regarding Momma Kelly and Aunt Marie. I would have liked even a throwaway line about it. But, it was not addressed or prepared as it should have been.
Hey, they finally digitized the books!!
As for grown-up Diana, Yowsa! I want THAT show....NOW!!!! They couldn't have made a better choice for what Hanna Lloyd might look later in life!! I like that the triplets, Diana and Kelly are in the Wesen-fighting business. I guess Nick and Adalind were good influences on Diana!