Ungoliant and Melkor
 

what would of happened if ungoliant had suceeded in killing melkor, I know she would of devoured the silmarils and probably melkor aswell but what would of happened after that

Good question. My guess would be that if she defeated Melkor, she would not devour him, but would certainly consume the Silmarils. They probably would have had a similar effect on her as they had on Carcharoth, only magnified since she was obviously a stronger being than Carcharoth. Who knows what evil she could have done, or who would have had the power to stop her?

Ungoliant, or any being in Arda, would not have been able to kill Melkor. It took the combined might of the Valar just to chain him.

If the Balrogs had not come to drive her away, I don't think that she could have done much more damage to Melkor than she already had.

But she was made vastly more powerful, because Melkor had added his strength to her - so I think she could, and would, have eaten him. Then the Charcaroth effect...also, she would have grown huge...and I daresay covered Middle-earth in unlight, fuelled by the maddening power of the Silmarills. Ironic. ;)