I've already purchased fighting games to replace MK9 for the most part. I still play it once in a blue moon, just to keep my Stryker flowing.
The online is crap, and we all know this. That's what will keep me from playing MK9, not Injustice.
MK9 offline with friends is still fun though, but I do prefer playing SF4, P4A, and DOA5 with my friends, since they just seem more friendly towards casual gameplay.