1. So you must successfully cast 2 spells. Any of them failded/unbound and all the plan will cripple.
2. You have only one reliable +1 - from Astrolith. Chance to get constellation is 1/3 - very unreliable. Casting curse of fates may be easy, but it is still can be unbound and will apply only to one roll. This means you need to take Vast Intellect instead of Great Rememberer.
3. Spell portal is good at it, but still don't grant you infinite range. There is still a chance it won't be enough, but OK, assuming that you managed to cast it.
4. Why are you saying it like if you go second, you automatically have a double turn? Lose the roll, and you are screwed.
5. If you go first the turn after, you cannot move Pendulum. If you go second, Morathi will simply move out of the line.
6. You cannot cast endless spells from arcane vassal.
7. Don't forget she has 6+ save from MWs. After all lucky saves you made above, you still have another one. If you deal less than 3 wounds, you just won't kill her in the following turn - she will be left with 1.
In short, dice gods must be really on your side to pull this out. And if they are on your side, why bother with strategy?