So I logged onto my mage today and while out questing and doing dailies I noticed an empty spot on my casting bar. No Evocation. It's not even in my spell book. I still have the glyph. I did some searching and see people are still using it and how is that possible?
Rune of Power replaces evocation. If you go with either of the other two level 90 talents, you get the spell.
Also to clarify why it dissappeared, if you have invocation, but then retalent to rune of power. Evocate will still stay on your bars just grayed out. If you log off, it will then switch off of your bars, hence its dissapearence.