Why are you assuming the ward was never cast? The only difference is the caster. Quan Chi doing it instead of Sindel to cover her murder, or even using her murder to fuel the casting works in exactly the same way. Only the intention changes.
Again, I feel dirty defending the evil Sindel thing, but this is absolutely not a problem. It becomes another case of "Quan Chi Did It," which is so cliche in the franchise at this point that I would prefer we didn't, but everything in the set up for the original tournament carries on just fine.
The bigger problem is trying to justify the heel turn in light of her previous behavior in MK3 and Deception, where she is unquestionably a goody goody. There's no way this Sindel and that Sindel coexist. So something fishy happened there. I mean, if I was really inclined, I'm sure I could use Kronika to justify it in some way, but I don't care to. And I'm not sure NRS cares either, this is the version of the character they are using for MK11 and that's that.
This got me thinking. A lot.
Follow me here, because I think I figured out a way to make this make almost sense.
Now...thinking about WHY Quan Chi could possibly want to cast the Ward, or ways it could still happen with Evil Sindel that would make us all happy, made me insane for a bit...but I have a theory.
It dawned on me that he could easily have something to gain from Earthrealm staying in one piece. Example: maybe he needed Shao Kahn to NOT conquer Earthrealm, because of something to do with the Kamidogu and resurrecting the Dragon King's Army, and it can't be done if Kahn assimilates Earthrealm into Outworld. Something like that.
It would make sense if it didn't lose its legs completely in a world where Sindel was evil the whole time, so I tried to MK logic my way around it.
With Good Sindel, it could have easily gone that Quan Chi picked up on Sindel's fear and dread and so on and put the idea in her head. The act itself maintains all nobility, no one suspects him, Sindel's character is preserved. But with Evil Sindel...I don't see how Quan Chi kills Sindel and makes the ward without Kahn bashing his head in, if there's even canonically a ward anymore at all.
The ONLY thing I can think of that could run this back and rationalize it...taking into account that this IS Mortal Kombat and while one is encouraged to bend reality, things won't always make perfect sense...is if Quan Chi had been in with Kronika, who can pull people through the sands of time from who knows where, from the very beginning as well.
If he had been shown his whole timeline, he would have been able to arrange everything as close to perfectly as possible. Hence the forever frustrating "Quan Chi Did It" answer for everything; maybe, he really did do EVERYTHING, to get his ultimate result, but in an even more convoluted way than Liu and Fujin.
It could very well be that this Sindel may not be the original Good Sindel at all.
Perhaps, in exchange for what he's seen, Quan Chi led Kronika, who has already been proven to be insanely powerful but not omnipotent, to strike a deal with Havik in Chaosrealm, to use the power of the Tempest to find a version of Sindel (and maybe also Shao Kahn) from a different reality where she WAS evil, and that THAT Sindel is one he reanimated into the Revenant to set the trap for later down the line, and the original Sindel is being held prisoner by Havik for some insane purpose, in that giant fucking prison in Chaosrealm that you couldn't get into until after you beat Konquest, where Kira is wandering around trying to regain her memory. Quan wants his army, Kronika wants her New Era, and Havik wants chaos everywhere. They could all win.
That convoluted mess of words is the only way I can rationalize Evil Sindel.
The part about this game that has had me absolutely spun since they introduced the time travel...is that if you hold it up against the original games, and the things that happened that made no sense back then - the characters you'd run into traveling between realms, people being in places and times they had no place being, and almost most importantly: The Pit Of Goo, where you find the Chaosrealm Kamidogu and suddenly Shujinko loses years of his life in a matter of moments, which was the first appearance of a timewarp in the MK timeline and things definitely seemed a bit out of order after that...if you take these two seperately illogical stories, and tie some of the knots together, it can almost add up. But not a whole hell of a lot of current players have played the 3D games, and are not aware of a lot of the stuff that's already in the books, so I can see how it wouldn't come up often.
But it could be done.