There is one main thing everyone must consider when factoring in if the the stab to Monet's Heart did in fact kill her.....And yes, she was stabbed, directly in the heart, and the panels shown leave very little room for debate.....But It does not mean the Stab killed Monet...The one thing that could have saved Monets life (And it is very plausible) is the Cube that was encasing it. When a person's heart is punctured in a manner that doesn't cause the heart to explode (Ex. a bullet), one of the very first things they do is immediately lose consciousness, but they don't die right away. The heart's main function is to continuously keep the blood pumping throughout the body, which in turn keeps the brain functioning. When the heart is pierced, it can no longer steadily keep the blood flowing, which in turn shuts the brain down. One of three things happen when your heart is punctured, you either become Brain dead, and die, or if the puncture is big enough, you bleed out and die before going brain dead, or by some miracle, you make it to a doctor in time, and survive...
This is where the Cube, and the panel you showed @Syphin comes into play. As we can clearly see, Ceasar did infact remove the spike from Monet's heart, and it was logged in the ground next to the cube. What we can also see, is that there is no longer any blood spilling out from the cube, in the same exact panel. Now I don't know exactly how the cube works, but it is possible, that the second Caesar removed the Spike, the cube closed back up, minimizing the blood loss from Monets heart, just in time to get the blood pumping back through her body, and keeping her alive.
Now I'm not saying Monet is alive or dead....But I figured I'd offer my input on how I believe it's possible she could have survived. Remember, the Ope Ope no Mi, is one of the most Haxed Devil Fruits in existence, and I'm sure Law wouldn't have given up his heart so easily if he knew that if that cube was punctured in any way shape or form, it would have resulted in his immediate death.....
And apparently you have a 1 and 3 chance of surviving being stabbed in the heart.