What Ultear's done is start a butterfly effect. One minute role back, and knowledge granted of that minute. Characters used that knowledge to save their own lives, and avoid taking heavy blows. So now instead of being dead, Gray and Bacchus are available to help turn the tide against the mini dragons. Gajeel no longer takes a blow that turns his fight against him, keeping the dragon from winning and breaking through to attack others. Etc and so forth.
In short, the one dragon spawned the smaller ones.
Also, being shot through the heart is more an instant guarantee of death than an instant death. An injury like the final shot would be an instant kill, but all the others would require him to lose enough blood for his various body systems to no longer be able to function, then a moment for everything to give out. If he were sufficiently in shock from the attack then he might not notice what went on around him after that, but he would have at least remembered the other attacks, save possibly the last, for the aforementioned reason. Not that it matters, really. Merudy was the one who recalled where the attack would come from so Gray could see and block it.
I've got a bit of free time at the moment, so I'll go ahead and give a bit more of an example of the butterfly effect at work here.
Before Ultear rewound time:
-Bacchus misjudges an attack from a mini dragon and fails to block it and gets a claw buried in his chest for his mistake. He dies and the mini dragon moves on.
-It moves on to encounter Sabertooth, preparing for an attack of a large group of mini dragons from a different direction.
-Since Minerva's MIA and Sting and Rogue are fighting dragons, Rufus and Orga are their only power houses left.
-Like the mini dragon that first hit Gray, it launches a surprise attack that kills Rufus.
-Confused, frightened, and demoralized at the loss of one of their strongest, Sabertooth's attention is divided between the group about to hit them, and looking for the one that got Rufus.
-With one of their two best AoE (area of effect) attackers gone, and their attention divided, most of the group of mini dragons reaches Sabertooth to engage them
-Without Rufus and his ability to launch a precision attack against multiple targets, Sabertooth is unable to recover, gets overwhelmed, and wiped out.
-Without Sabertooth to soak up mini dragons, groups of them that would otherwise be wiped out by Sabertooth attack weaker guilds who are unable to deal with them and get wiped out in turn.
-The guilds slowly get over run, the DS distracted by their friends dying lose their fights, and F. Rogue and the dragons win.
After Ultear rewound time:
-Bacchus sees the attack that kills him ahead of time, blocks it, kills the mini dragon, and moves on.
-Without the mini dragon killing Rufus, Sabertooth is undistracted from the large group about to hit them.
-Rufus and Orga tear great holes in the group before it can reach Sabertooth.
-Sabertooth easily holds back the survivors that manage to engage them, and a precision attack from Rufus makes mopping up the survivors easy.
-Sabertooth moves on to wipe out more groups.
-With less pressure on them, the weaker guilds win their fights and move on to help others
-The guilds wipe out the mini dragons, and undistracted the dragon slayers either win their fights, or hold out until Future Rogue is defeated and the dragon's lose interest in obeying his orders.
Thus the difference between one small attack being blocked or not block turns the tide of the battle one way or another.
For further reference, read these:
That is how turning back one minute can turn the tide of battle.
well her death is sad at least she is now which her mother lool there should be a mini-adventurers with her and her mother
Thinking about it just killing urtear like that would be kinda unfitting for mashima. The guy is all about the happy endings to a great degree. There are sad moments but he rarely passes on an opportunity to give someone a random nice ending... I am think that urtear will live for a while and after she "dies" she will actually travel in time to the past to a moment where she can reunite with her mother. She would basically get her wish and a fresh start.
So Ultear dying here would not be that far out of line with the rest of the series.