what would've happened if snow didnt poison cora's heart?

She would turn good and mostrar más amor towards Regina. I don't think Regina would have made truce with the charmings since she would probably be spending más time with Cora. And Cora would probably have killed Greg por now, corazón o no heart. Nobody messes with her daughter and gets away with it!

Cora would've actually loved Regina then killed Rumple and became the dark one. She would've killed Snow, Charming, and Emma (possibly Neal if she found out he was Henry's father), kidnapped Henry, killed Ruby in the process, killed Greg, if Tamara came to town she would've killed her, and caused pain and suffering for all of Storybrooke and everyone would blame Snow for not being able to kill Cora.

Cora wasn't exactly a good person before she took out her corazón so no one really know what kind of person she would have been when she got it back. My best guess is that she would have been capable of truly loving Regina and finally make her daughter her first priority rather then segundo to power. She still might have killed the Charming's in an attempt to make her daughter happy. I don't think she would have been able to kill rumple after remembering her amor for but I don't think she would have been able to cure him either and he would have died taking the power of the Dark One with him.