Rooting is like gaining admin access to your phone. It technically voids your warranty as there is a lot that can be messed up by having root access.
Yes, you can return the phone to stock using Odin.
Personally, I will never buy another android phone without being able to root it, but I'm aware if the risks involved. Ultimately, I would recommend reading everything you can on rooting and going from there. Don't do it until YOU are ready.